As all men naturally desire to know the truth, so there is in men, by nature, the desire to shun errors and to refute them when possessed of ability to do so. Among all errors, moreover, the one that seems to be especially unbecoming is the error about the intellect; for we have been born to know the truth by the power of this intellect through the avoidance of errors. Of late there has sprung up an erroneous doctrine about the intellect on the part of many men who take their starting point from certain works of Averroes. They assert that the intellect, which Aristotle called the possible intellect (he also inaptly called it "immaterial"), is evidently a kind of substance separate, by its very nature, from the body, yet in some way united to the body as its form; and further, that this possible intellect is one for all men. Against this doctrine we have already written much. But since the boldness of those in error has not ceased to assail the truth, it is our intention once more to direct an answer to this false teaching in order that its error may be manifestly confounded.

At this time it will not be our method to show that the aforesaid position is erroneous as being repugnant to the truth of Christian faith: this is at once sufficiently evident to anyone. For if there is no diversity of intellect among all men, and the intellect appears to be the only incorruptible and immortal part of the soul, then it follows that after death nothing of the souls of men survives except the one common intellect. Thus would be destroyed any possibility of retribution, of rewards and punishments, or any diversity in recompenses. However, we intend to show that their position is not less in conflict with the principles of philosophy than it is with the certain testimony of faith. Since for certain men concerned in this matter the words of the Latin philosophers have no savor, and since they claim to be followers of the Perpatetics (though of their books on this subject they have seen none, except those of Aristotle, who was the founder of the Peripatetic school), we shall point out that their position is altogether at variance with his words and express opinion.

First of all, there must be acceptance of the definition of the soul which Aristotle proposes in II De Anima, saying: "The first act of a physical, organic body." And lest, perhaps, someone may say this definition is not altogether applicable to all souls because of what Aristotle previously had conditionally stated; namely, "that it is necessary to predicate something that is common to all souls" (which they would understand to mean that such a thing cannot be), the following words of his must be noted. He says: "We have now given an answer to the question, What is soul—an answer which applies to it in its full extent. It is substance in the sense which corresponds to the definitive formula of a thing's essence. That means that it is the essential whatness of a body" (i.e., of a naturally organized body).

Lest it be thought that from this universal definition the intellectual faculty is excluded, this presumption is dispelled by what he afterward says: "The soul is inseparable from its body, or at any rate certain parts of it are—for the actuality of them is nothing but the actualities of their bodily parts. But, in truth, as regards other of its faculties, nothing prevents separation; since there are acts which belong to no body whatever." But this cannot be understood except of those acts that pertain to the intellectual faculty, namely, intellect and will. Wherefore it is clear that of the soul, which Aristotle had previously defined universally and called "the act of the body," certain faculties are the act of certain parts of the body; but other faculties are the act of no body. For it is one thing that the soul should be the act of the body, and another thing that a part of it should be the act of the body, as will be explained later. Hence also, in the same chapter, he shows clearly that the soul is the act of the body, since certain of its faculties are the act of the body, when he says: "One must consider in regard to the parts what has been said of the whole."

Moreover, in subsequent passages it appears even more clearly that the intellect is included under this general definition, as is shown by statements that follow. For, although he had previously given sufficient proof for the fact that the soul is the act of the body (since, if the soul is separated from it, the body no longer is in act as a living thing), he reiterates his position, because a thing may be called "actual" by the presence of a thing other than its form, if that thing were only an efficient cause; just as a combustible thing catching fire by proximity to something burning is "in act," and as a movable thing is "in act" when by the power of a mover it is set in motion. Hence doubt might arise in some one's mind as to whether the body is alive, or in act, by the effect of the soul's presence as any movable thing is moved by the power of an extrinsic agent, or whether it is in act as matter is, by its union with its form. There was a special need for Aristotle to clarify his position, since Plato had held that the soul was not united to the body as its form, but rather as a "mover" and "governor," as is evident from Plotinus and Gregory of Nyssa. I may certainly cite these men, since they were not Latins, but Greeks. The uncertainty of this problem, therefore, the Philosopher implies by what he afterward adds to earlier statements, saying: "We have no clear light on the problem whether the soul is the actuality of tis body in the same sense in which the sailor is the actuality of the ship."

Therefore since, even after previous explanation had been given, some doubt remained, he added a supplement, saying: "Thus figuratively a definition and description of the soul is given," because no one has yet demonstrated the truth to the point of certainty.

In order, therefore, to remove this doubt, he proceeds to reveal the things that are, of themselves and according to their nature, the more certain by means of the things that are less certain in themselves, but more certain as far as we are concerned; that is, he undertakes his demonstration through considering the effects of the soul, effects that are its acts. Hence he immediately makes distinctions in the operations of the soul, saying that an animate thing is distinguished from an inanimate by the fact of living, and that there are many things that pertain to life: namely, understanding, sensation, and change, both change of place and alteration connected with nutrition and growth; so that anything in which any of these characteristics is found may be said to "live." Furthermore, having shown how these powers are related one to another—how a being possessing one without the others is said to live, and how one can exist without the other—he concludes in this manner: The soul is the source of these phenomena and is characterized by them, namely, by the powers of self-nutrition, sensation, thinking, and motivity; and all these can be united in one and the same subject, as in man.

Moreover, since Plato had supposed that there were diverse souls in man according as different operations of life were found in him, he had inspired doubt whether each one of these were a soul, per se, or only a part of the soul; and if they were parts or faculties of the one soul, whether they differed only according to reason, or whether they were distinct according to place, that is, in organic location. And Aristotle added: "Regarding certain of these questions, there seems to be no difficulty, but others possess uncertainty." For, he pointed out, one thing is made clear about the things that pertain to the vegetative soul and the things that pertain to the sensitive soul by this fact: that plants and certain animals from which a part has been severed continue to live, and in each part all the operations of the soul which had gone on in the whole organism appear to endure. But of those questions that are doubtful he makes note when he says: "Concerning the intellect and power of foresight, nothing is yet distinctly evident." This statement he does not make because he wishes to show that the intellect is not a faculty of the soul, as the Commentator and his followers have perversely implied. For evidently this does not follow upon what he had previously said, that "some things, indeed, are uncertain." Therefore he must be understood to have meant that it is not as yet evident whether the intellect is the soul or part of the soul; and, if a part of the soul, whether it is distinct as to place, or only according to reason.

And although he says the matter is not yet clear, he subsequently adds what seems at first sight to be true: "But it seems that the soul is of another genus." Now, this ought not be interpreted as the Commentator and his school have perversely explained: namely, that he said this because the intellect is equivocally spoken of in regard to the soul, or because he could not harmonize his conclusion with the previous definition; but how it ought to be interpreted is evident from what follows: "In this respect it pertains to the intellect to be 'separate': namely, as the eternal is distinct or separate from the corruptible." In this, therefore, consists the fact that the intellect is another genus, because our intellect in this respect appears to be in a certain way eternal, but the other parts of the soul, corruptible. And because the corruptible and the eternal do not seem capable of union in the one substance, it seems that this one of the soul's faculties, namely, the intellect, should be separate, not indeed from the body (as the Commentator falsely maintained), but from the other faculties of the soul, and thus not communicate in the same way in the one substance of the soul.

That this should, in truth, be the interpretation is clear from what follows: "The other parts of the soul, it is evident, are not separable according either to substance, to reason, or as to place.'' Concerning this, inquiry had previously been made, and this, from the above cited passages, has been proved. Moreover, that the separability of the intellect should be regarded as meaning separability, not from the body, but that of the potentialities of the soul from one another, is evident from what follows: "It is certainly evident from reason that these powers are mutually distinct. Clearly, sensation is one thing, and opinion another." Hence he points out plainly by this determination his answer to the question proposed above. For the previous inquiry had been as to whether one part of the soul were distinct from the others according to reason only, or by actual location. Having dismissed this question as regards the intellect, concerning which he makes no definite answer, he says that, in regard to the other parts of the soul, it is clear that they are not separable as to location, but are distinct according to reason.

In maintaining that the soul is determined by its vegetative, sensitive, intellective, and motive powers, he wishes to show that in regard to all these faculties the soul is united to the body, not accidentally as a pilot in a ship, but as form is united to matter, that is, substantially. Thus it will be made manifest what the soul is in general, this manifestation having been made only in figurative language heretofore. Moreover, he further proves what the soul is by considering its operations as follows: Evidently that by which anything is first enabled to operate is the form of that operator just as we say we know by means of the soul and by means of science; although that we know by means of science is prior [in consciousness or reflection] to the fact that we know by means of the soul, because we do not know through the soul except in so far as it possesses science. Likewise we are said to be healed in body and in health, but in health primarily. Thus also it is evident that science is a form of the soul, and health a form of the body.

And in this way he proceeds. "It is the soul by or with which we live." This he says because the soul is vegetative; "and that principle by which we experience sensation," because it is sensitive; "and that by which we are moved," because it is capable of motion; "and that by which we think," because it is intellective. And he concludes: "Because it will ever be a certain nature and species, but not as matter and a subject." Evidently, therefore, as he said above, the soul is the act of the physical body, so here he concludes that it is not only the act of the vegetative, sensitive, and motive powers, but also the act of the intellect. Hence this was the opinion of Aristotle: that by which we understand is the form of the physical body. But, lest some one should think Aristotle did not say that that by which we understand is the possible intellect, but something else, then, plainly this is refuted by what he states in III De anima concerning the possible intellect. There he says: "By mind I mean that whereby the soul thinks and judges."

But, before we reach these words of Aristotle, which are in Book III of De anima, we should pause somewhat longer upon those remarks of his which are in Book II of De anima, so that from various statements assembled for comparison there may be clearly deduced what his opinion was about the soul. Now, after he had defined the soul in general, he began to distinguish its faculties; and he says: "The powers of the soul are vegetative, sensitive, motive, and intellective." That the intellective faculty is the intellect, he states clearly in what he adds later in explaining this division of powers: "One of them is, indeed, intellective, and is the intellect, as in men." He wishes, therefore, to make clear that the intellect is a power of the same soul which is the act of the body.

And that he had called the intellect a faculty of this soul; and, furthermore, that the definition of the soul is commonly inclusive of all its parts, is evident from his conclusion: "It is now evident that a single definition can be given of soul only in the same sense as one can be given of figure. For, as in that case there is no figure distinguishable and apart from the triangle, etc., so here there is no soul apart from the forms of soul just enumerated." Hence no other soul is to be sought for in addition to the ones already discussed, to which the definition of the soul given above is commonly applied. In the Second Book, Aristotle reveals nothing further of his theory about the intellect except that he adds, farther on, that ratiocination and understanding are the highest powers, and that they are also the least because, indeed, they are in very few creatures, as hereafter will be made clear.

But because there is a great difference in operation between the intellect and the imagination, he speaks in regard to the speculative intellect of "another nature"; yet he postpones discussion of this question to the Third Book. No one, however, should say (as Averroes falsely states) that Aristotle declares that there is "another reason" or "nature" in the speculative intellect because the intellect is not in the soul, or any part of the soul. This is immediately excluded as a possible interpretation in the beginning of the Third Book, where he resumes his discussion of the intellect; for he speaks here as follows: "Concerning that part of the soul, by which the soul possesses knowledge. and wisdom." Neither should anyone say, as some have dreamed of doing, that Aristotle says this only according as the possible intellect is distinguished from the active. For this passage occurs before Aristotle proves that there is a possible as well as an active intellect; wherefore he speaks here of the intellective part of the soul in common, according as it comprises both the active and the possible intellects (even as in, the Second Book he clearly distinguishes the intellective from the other parts or faculties of the soul, as has been said).

Moreover, the admirable precision and order of Aristotle's method of procedure must be observed. Now, in the Third Book, he begins his treatise concerning the intellect, which, in Book II, he had left undecided. There he had previously allowed two things to remain uncertain.

First, the question whether the intellect is distinct from the other faculties of the soul only according to reason, or whether it is also distinct as to location. This he had dismissed indefinitely when he said: "We have no evidence as yet about mind or the power to think."

This position he at first resumes when he asks: "Whether in existence it is separable (from other parts of the soul), or is inseparable from the quantity of the body but distinct or separable according to reason." In this passage he employs the phrase, "secundum magnitudinem" to indicate what he had previously spoken of as "separabile loco."

Secondly, he had left in uncertainty the difference of the intellect as compared to the other faculties of the soul, when in conclusion he said: "In regard to the speculative intellect, however, there is another nature." This he straightway questions when he says: "What kind of difference the intellect possesses must be considered." He undertakes to assign it such a difference as could stand according to both of the premises already proposed: namely, whether the soul is separable spacially in respect to certain parts of the body, or not; and this intention he himself plainly enough indicates by his manner of speaking: "Turning now to the part of the soul with which the soul knows and thinks (whether this is separable from the others in definition only, or spacially as well) we have to inquire what differentiates this part and how thinking can take place." From this it is evident that he did not intend to show that the difference was one of substantial separation from the body; for this position could not be maintained in view of both the alternatives proposed, but he intended to assign to the intellect a difference in mode of operation. Hence he continues: "And according to what manner it comes to understand." Consequently, by means of those statements which we are able to gather from the words of Aristotle himself, it is evident, thus far, that he wished the intellect to be regarded as a faculty of the soul, which is the act of the physical body.

But since, from certain other words, Averroes has tried to make it appear that Aristotle meant that the intellect was not the soul, which is the act of the body, nor any part of such a soul, further statements must also be attentively considered. Immediately after raising the question as to the difference between the intellect and sensation, Aristotle inquires in what way the intellect is like the senses and in what way it differs from them. Now, previously he had concluded two things about sensation: namely, that a sense is in potency to sensible objects, and that a sense is impaired or even destroyed by the excellence of sensible objects. On this point, therefore, Aristotle makes inquiry, saying: "If to understand is the same as to experience sensation, or to be passive to something, then in the same way the intellect will be passively impressed by its intelligible object, and will be overpowered by the excellence of that object, just as the senses are by the too-great excellence of sensible things, and in like manner of other things." Thus the question is this: Is the act of understanding something quite similar to that of experiencing sensation, or is it, on the contrary, different in this respect, that it is not passible?

To this question, he immediately answers (deriving his conclusion not from previous statements but from those which he makes subsequently, which later statements are, however, clearly evident from an analysis of the former) that this part of the soul ought to be impassible and not subject to the same alteration or corruption as the senses. Yet it has a certain passivity, but this is of another sort, according as the term, "to understand," commonly means "to be passive." In this respect, therefore, it differs from sensation. But at the same time he shows how it agrees with sensation: for, indeed, this part must be capable of impression by intelligible species and be in potency to species of this kind, and not, by its own nature, in act—even as he had previously stated that a sense is in potency to sensible objects and not, of itself, in act. From this he concludes that the intellect must be related to intelligible objects just as a sense is to sensible things.

Now, he stated this in order to reject the opinion of Empedocles and other ancient philosophers who taught that the knower is of the same nature as the thing known, so that, being composed of earth, we know earth, and being also of water, we know water. Aristotle, however, had shown previously that this is not true in regard to the senses, because a sense faculty is not in act, but only in potency to that which it experiences as a sensation; and the same, he says, obtains in regard to the intellect.

There is, nevertheless, this difference between the senses and the intellect: that each sense is not capable of experiencing all sensations, but sight is in potency only to color, hearing to sound, and so of the others; whereas the intellect is, absolutely, empowered to know all things. The ancient philosophers, thinking that the knower had to possess the same nature as the object known, had said furthermore that this fact, that the soul was capable of knowing all beings, must be on account of its being composed of the principles of all things. But, because Aristotle had now proved by comparison with sensation that the intellect is not in act as regards what it comes to know, but in potency only, he concludes, on the contrary, that since the intellect knows all things, it must be without any mixture; that is, not composed of all the elements, as Empedocles had stated.

To support this theory, he also calls upon the testimony of Anaxagoras, even though he had spoken not of this same human intellect, but of that mind (Nous) which moves all things. But just as Anaxagoras had declared that that intellect, in order to govern all things by setting them in motion and keeping each in its proper course, must be simple, or unmixed, so we can say of the human intellect that it must be simple in order to know all; and this Aristotle consequently proves, and the Greek text says: "Now, that which is within, evidently hinders and prevents the extraneous from entering, as can be understood by a comparison with vision." For if there should be any color intrinsic to the pupil of the eye, that interior color would prevent the seeing of the color outside, and in some manner hinder the eye from seeing other things.

Likewise, if any nature of those things which the intellect knows—for example, earth or water, warmth or cold, or anything else of the sort—were intrinsic to the intellect, that intrinsic nature would be an obstacle to the intellect, and in some way prevent its knowing other things.

Since, therefore, the intellect does know all things, Aristotle concluded that it could not possess any determinate nature derived from the natures of sensible things which it knew, but that its nature was constituted by this alone, that it must be possible of determination; that is, that as regards its nature it must be in potency to those things which are intelligible, but become active by understanding them in act; just as the senses are made to be in act by the sensible in act, as he had previously said in the Second Book. He concludes, therefore, that the intellect, before understanding renders it "in act," is not actively any of the things which exist—a conclusion which is contrary to what the ancients claimed: namely, that it was actually all things.

Moreover, because he had mentioned the statement of Anaxagoras in which he speaks of that intellect which governs all things, Aristotle, lest anyone believe that he had drawn his conclusion about that same intellect, employs this manner of explanation: "Anaxagoras called this the soul's intellect. I speak, however, of that intellect by which the soul thinks and understands, which is actively none of those things which exist before they are understood." From this, two facts are evident.

First, that he certainly is not speaking here of an intellect which is some kind of separate substance, but of the intellect which, as he said above, is that power and faculty of the soul by which the soul understands.

Secondly, the fact that he had previously proved; namely, that the intellect has no nature which is determinate in act.

He has not yet proved that it is not a power existing in a body (as Averroes says), but this he immediately concludes from the foregoing, when he says: "Therefore the rational faculty has no admixture of that which is corporeal." This second statement he proves by means of the first, which he previously explained: namely, that the intellect possesses actively none of the natures of sensible things. From this it is evident that there is in it no union with anything corporeal; for if it were intermingled with some bodily substance, it would possess some kind of corporeal nature. And he adds: "For indeed, a thing would become some kind of thing, either warm or cold, if it were united to a bodily organ, Just as m the case of the sensitive faculties." Now, each sense is proportioned to its own organ and is bound, as it were, or restricted to its own nature. Hence according to the immutability of the organ, the operation of each sense is immutable. Thus, therefore, he understood that the intellect was not blended with the body; namely, that it has no organ as have the senses.

Moreover, that the soul's intellect has no organ is clear from the statement of those who say that the soul is the locus of the intelligible species (accepting the term "locus" broadly in the sense of Plato, as meaning that which is all-receptive); unless to be the locus of the species is not proper to the whole soul, but to the intellect alone. For the sensitive part of the soul does not receive species into itself, but in an organ. The intellective faculty, however, receives them in no organ, but in itself. Moreover, the locus of the species is not such that it possesses these in act by its nature, but that it is in potency to possess them.

Since, therefore, he has shown what befits the intellect, by means of comparison with the senses, he now returns to what he had first said: that the intellective faculty must be capable of receiving species; and so, with admirable subtlety, by means of a likeness, he concludes to dissimilarity. Hence he subsequently shows that the passibility of the senses and that of the intellect are not similar by the fact that a sense faculty is disturbed by the excellence of a sensible object, but the intellect is not overpowered by the excellence of its intelligible object. The reason of this he assigns as derived from the preceding discussion: namely, that the sensitive faculty is not incorporeal, but the intellectual is, being "separate."

This last word, "separate," some have especially seized upon as a prop for their error, for they would interpret him to mean by it that the intellect is neither the soul nor a faculty of the soul, but a separate substance; but they too quickly forget what Aristotle said but a little before. Now, just as here he says that the sense faculties are not incorporeal, but the intellect is separate, so previously he had said that the intellect would be of a certain quality, either warm or cold, if it possessed any organ, as the sense faculties do. By this method of reasoning here, he is stating that the senses are not incorporeal, but the intellect is "separate," since a sense faculty has an organ, but the intellect has not. Most evidently, therefore, it appears from the words of Aristotle that, without any doubt, this was his opinion about the possible intellect: namely, that the intellect is some part of the soul, which is the act of the body; but that, nevertheless, the soul's intellect has no corporeal organ, as have the other powers of the soul.

Moreover, how this can be—that the soul is the form of the body, and yet that some power of the soul should not be a power of the body—is not difficult to understand if we consider that same situation in regard to other things. For we see, in many cases, that a certain form is the act of a body composed of a mixture of elements, and yet it has a certain power which is not that of any of those elements, but which belongs to such a form from some other principle: namely, from a heavenly body, just as a magnet has the power of attracting iron, and jasper has the power of checking the flow of blood. And we see that, by degrees, those forms which are the nobler possess powers which more and more exceed those of matter. Wherefore the highest of forms, which is the human soul, possesses one power which altogether transcends the material body: namely, the intellect. In this way, therefore, is the intellect "separate," since it is not a corporeal power, but a power in the soul; though this same soul is the act of the body.

Neither do we say that the soul, in which the intellect resides, so excels its material body that it does not require to be in a body, but only that the intellect, which Aristotle calls a power of the soul, is not the act of the body. Nor is the soul the act of the body through the mediation of its faculties, but it is itself, per se, the act of the body, giving to it its specific nature; whereas some of its faculties are the acts of certain parts of the body, perfecting them as regards certain operations. Thus that faculty which is the intellect is the act of no part of the body, since it requires no corporeal organ.

And lest it seem to anyone that I say these things according to personal interpretation, departing from the intention of Aristotle, the words of Aristotle himself can be cited which expressly state the same opinion. For, in II Physic. he asks just how far one ought to know a species and what a thing is: For it does not pertain to physics to study every form. He subsequently gives as his answer: "In the same way as a physician must know a nerve, or as the smith must know bronze: that is, in view of a certain end." And to what "end" he has reference, he later shows: "In view of whatever the purpose of each is." This is as if he would say: The physician studies the nerve only inasmuch as it pertains to the health, on account of which the physician considers the nerve; and likewise, the smith considers the bronze only in view of his craft; and since the physician considers the form so far as it is in matter—for thus it is the form of a body subject to change—in like manner, it must be understood that natural science considers a form only inasmuch as it is in matter.

The terminus of the physicist's consideration of forms is in those forms which are in matter after a certain fashion, but which, in another way, are not in matter. For these forms are on the boundary line of separate and immaterial forms; wherefore, he adds: "Regarding this, the consideration of the physicist is, indeed, of forms which are separate, but as they are specific forms in matter." What these forms are, he indicates, saying: "Man generates man from matter,—man, that is, and the sun." The form of man, therefore, is in matter and yet separate. It is in matter inasmuch as it gives existence to the body, and thus it is, indeed, the cause of generation; but it is separate as regards that faculty which is properly that of man: namely, the intellect. It is not impossible, therefore, that a form should be in matter and that a faculty of it should be separate, as has been shown in respect to the intellect.

There are still some, however, who undertake to show in another way that the opinion of Aristotle was that the intellect is not in the soul, that it is not a faculty of the soul which is united to the body as its form. In many places, Aristotle says that the intellect is eternal and incorruptible, as, for example, he declares in II De anima: "This befits a separate form alone, as eternal is distinguished from corruptible." And in Book I, where he says: "The mind seems to be an independent substance, and to be incapable of being destroyed." He has also stated in Book III: "The separated form alone is that which truly is, and this only is immortal and eternal." This last quotation, however, some do not apply to the possible, but to the active intellect. From all these passages it is clear that Aristotle wished it understood that the intellect is something incorruptible.

Yet it seems that nothing incorruptible could be the form of a corruptible body. For, indeed, it is not accidental to this form, but pertains to it essentially to be in matter; otherwise from the union of matter and form there would result only an accidental whole. But nothing can exist without that which belongs to it essentially; consequently the form of the body cannot exist without the body. If, therefore, the body also is corruptible. Furthermore, forms separated from matter, and forms existing in matter, are not of the same species, as is proved in VII Metaph. Much less, therefore, can one and the same form, numerically, be now incorporeal, and now in a body. Hence, if the body is destroyed, the form of the body either will be destroyed or will pass into another body. If, therefore, the intellect is the form of the body, it seems to follow of necessity that the intellect is corruptible.

Now, it must be noted that this manner of reasoning influenced many philosophers: Gregory of Nyssa, for example, interpreted Aristotle in a contrary way by supposing that, because he had said that the soul is the form of the body, he judged it to be corruptible. Certain others, moreover, because of this same statement, have supposed that the soul migrates from one body to another. Still others have held that the soul possesses some kind of incorruptible body from which it is never separated. Hence it must be shown from Aristotle's words how it was that he judged that the soul was the form of the body, and yet judged also that it was incorruptible.

In XI Metaph., after he had explained that forms are not antecedent to their matter—because, just as at the time when a man is healed, simultaneously there is health; and as the figure of a bronze sphere is simultaneous with the bronze figure—he next inquires whether any form remains after the corruption of the matter, and he answers in the affirmative, according to the opinion of Boethius: "But it must be considered whether, in truth, anything does remain afterward apart from the matter. In certain cases nothing would hinder this being so, if the soul were of this order: that not all of it would remain—for, perhaps, that would be impossible—but that the intellect, of all its powers, would remain." Hence, it is evident, he says, that nothing would prevent the intellectual faculty of the soul, which is the form, from remaining after the body, even though it did not exist before the body. For, although he had said, absolutely, that efficient causes are antecedent, but not formal causes, he does not question whether any form might exist prior to matter, but whether any form could remain after matter; and he says that nothing would hinder this on the part of that form which is the soul as regards its intellectual faculty.

Since, therefore, according to the foregoing words of Aristotle, this form which is the soul could continue to exist after the body-not in its entirety, but the intellect-it remains to consider why the intellectual part of the soul should survive the body rather than the other faculties, and rather than other forms which do not survive their matter. The reason of this, indeed, can be gathered from the words of Aristotle himself. For he says in III De anima: "The separate [form] is that alone which truly exists, and that alone which is immortal and eternal." He seems, therefore, to assign this as a reason: that since the intellect alone seems to be immortal and eternal, it alone is separate.

But concerning what intellect it is that he here speaks of, there can be doubt. According to some, he is speaking of the possible intellect; according to others, of the active. But, that both these groups of interpreters are mistaken is evident if the words of Aristotle are considered attentively. For both the possible and the active intellect Aristotle had called "separate." It is certain, therefore, that anything he may say of either the active or the possible intellect individually can be understood as applying to the whole intellectual faculty, since it possesses no corporeal organ of operation, as is evident from Aristotle's own words.

Moreover, Aristotle had said in I De anima: If there is any way of acting or being acted upon proper to soul, soul will be capable of separate existence; if there is none, its separate existence is impossible. Rather [its existence] is that with which it shares a common nature. Since everything operates inasmuch as it exists as a being, so the mode of the action of each thing is conformed to its mode of existence. Therefore forms that have no operation except in conjunction with their matter do not themselves act; but it is the composite that acts through its form. Wherefore forms of this kind, properly speaking, are not; but something is possessed by them. In the same way as heat does not warm, but something hot warms; so also heat itself does not exist by means of that which has heat, properly speaking; but that which possesses heat does exist through that which is heat-in-itself. On this account, Aristotle says in X Metaph. that it is not truly said of accidents that they are "beings," but more truly that they are "of a being";

and the same reasoning is employed about substantial forms that have no operation when not united with matter, except that the principle of substantial existence belongs to this form. Therefore a form that possesses an operation of its own, according to any of its faculties, or a power independent of matter, is subsistent; nor does it exist by means of the existence of the composite, as do other forms, but rather the composite exists through it. Hence, if a composite is destroyed, that form which possesses existence from the composite is likewise destroyed. On the other hand, it would not follow that the destruction of a composite would bring about the destruction also of a form by whose existence the composite exists, and which does not owe its existence to that of the composite.

If, however, some one objects that Aristotle (I De anima) says: "To understand and to love and to hate are not its activities, not phenomena of the soul, but activities of him possessing the capacity to know and to love and to hate. Wherefore in case of corruption the soul neither remembers nor loves, for these things do not belong to it properly, but were common attributes, as the saying is"—then an answer is provided by the statement of Themistius who, commenting on this says: "Aristotle here assumes more the attitude of one in doubt than of one teaching authoritatively." Now, at this point, he had not yet refuted the opinion of those who said that the intellect and the senses are not different;

wherefore in this entire chapter he speaks of the intellect as of a sense faculty. This is particularly apparent where he proves the incorruptibility of the intellect by the example of a sense faculty that is not impaired by old age. Hence throughout he speaks conditionally and in a way to imply doubt as if seeking an answer, always linking things that pertain to the intellect with mention of the senses—a fact made especially evident by what he says in the beginning of this discussion: "We may admit to the full that being pained or pleased, or thinking, are movements (each of them a 'being moved')." If, however, anyone holds that Aristotle is speaking precisely, there remains this reply: that to understand is said to be an act of the intellect united to the body, not per se, but per accidens, inasmuch as the object of the intellect (the phantasm) is in a corporeal organ; but the act of the intellect is not exercised through a corporeal organ.

However, someone may inquire further and ask: "If the intellect is incapable of understanding without the phantasm, how will the soul have any operation after it has been separated from the body?" We reply that whoever raises this objection ought to know that the solution of this problem does not pertain to natural philosophy. Hence, in II Physic., when speaking of the soul, Aristotle says: "How the separable form will be related to other things, and what kind of being it is, is the task of first philosophy to determine. Now, the separated soul must be judged to possess a mode of knowledge other than that which the soul has while conjoined with matter"—a knowledge like that of other separate substances. Therefore, not without reason, Aristotle inquires, in III De anima, whether an intellect not separated from spacial magnitude can know anything that is separate.

By this question he gives us to understand that the separated intellect is able to understand something which the intellect which is not separate is incapable of knowing. In these same words, moreover, it is to be noted that, whereas he had formerly called both the possible and the active intellect "separate," so here he speaks of both as "not separate." For they are "separate" to the extent that their acts are, not the acts of any corporeal organ; yet they are "not separate" in that each is a faculty or power of the soul, which is the act of the body, as has previously been said. Furthermore, it is most certainly possible to show that Aristotle solved questions of this kind in those books which, from what he says in the beginning of XII Metaph., we are sure that he wrote concerning separated substances; and of these books I have seen fourteen, though they have not yet been translated into our language.

Accordingly, it is clear that his reasoning involves no necessary contradiction: It is essential to the soul that it should be united to a body, but by this it is restricted only accidentally, not on its own part, but on the part of the body, which is corruptible; just as, per se, bodies that are light or subtle have their place above the heavier, and it is essentially characteristic of these light bodies so to exist on high. But, as Aristotle says in VIII Physic., it may happen that on account of something weighing it down, such a body would, nevertheless, not be in its proper, higher place.

In this way, he offers the solution of the other difficulty. For, just as that which has a nature to be above other bodies differs specifically from that which does not have the nature to be so; and as that which essentially is thus subtle has its own same nature, numerically and specifically, whether it is in its proper place above others, or whether, on account of some impediment, it is not, so also two forms differ specifically if one of them has the nature to be united to a body and the other has not. Nevertheless, that having the nature to be united to a body will be, numerically and specifically, one and the same form both when it is actually united to a body and when, on account of some interference, it is not actually so united.

However, some still bring up, as a prop for their error, what Aristotle says in his book, De generatione animalium: "The intellect alone comes from without and it alone is divine." Now [those proposing the objection say that] no form which is the act of matter comes to that matter from without, but it is educed from the potency of matter. The intellect, therefore, is not the form of the material body.

They also say by way of objection that any form of a mixed body is caused by the elements; therefore, if the intellect were the form of the human body, it would not come from outside, but would be produced by its elements.

Some object further that it would follow that the vegetative and the sensitive souls would also be of extrinsic origin—a statement contrary to the opinion of Aristotle—especially if it is maintained that there is but one substantial soul whose powers are vegetative, sensitive, and intellective; since, according to Aristotle, the intellect is from an extrinsic source.

The solution of this difficulty, however, is at once evident from what has previously been said. For, although he said that any form is educed from the potentiality of matter, the phrase, "educed from the potentiality of matter," may be taken in two ways. In the first place, a form may depend on matter both for existence and for its operation; but, in another way, it may mean that matter must exist prior to form. Now, if the meaning is only that matter shall precede the form, it seems that the form could be considered to be "educed from the potentiality of matter." For if this is to say nothing else than that matter pre-exists in potentiality to a form, nothing hinders one from saying that corporeal matter pre-exists in potentiality to an intellectual soul, whence Aristotle in De generatione animalium says: The vegetative soul must be considered to be potentially possessed in semination and conception, before separation from the parent; but such souls are not in act until, having been conceived, they become separated, procure food, and carry on the functions of such a soul. For, in the beginning, these appear to have all their life as the life of the parent.

The same must be said also of the sensitive soul, and even of the intellectual. For, necessarily, all these souls must be considered to be in potency before they are in act, so that it may not have the same meaning for them to be "in potency" and "in act." Now, it has been shown, in regard to those forms that have no operation apart from their union with matter, that they ought to be such in the act by which they exist as that with which they are combined or mingled, and with which they co-exist, since they possess the selfsame existence; wherefore, as their total existence is directed toward concretion in matter, so they are said to be totally educed from the potentiality of matter. The intellectual soul, on the other hand, since it has an operation apart from the body, has not an existence directed solely toward concretion in matter. Wherefore it cannot be said to be educed from matter; rather, it exists by reason of an extrinsic principle. This is apparent from these words of Aristotle: "It must be concluded, however, that the intellect alone comes from without, and it alone is divine." And the reason for this conclusion he assigns when he says: "For no bodily operation shares in its operation."

However, I wonder at the source from which a second objection proceeds, namely, "If the intellectual soul is the form of a mixed body, it must be caused by a mixture of the elements, whereas no soul is caused by a commingling of elements." Now, Aristotle says, immediately after the foregoing words: "But every power or potency of the soul seems to participate another kind of body than those called the elements—one of a more divine nature. Truly, inasmuch as souls differ among themselves as noble from ignoble, so also the natures of bodies differ. For there is in the generating principle of all things that which makes them to become fecund principles of generation: for example, that which is called heat is not fire, nor any property of it, but a 'spirit' which is contained in the generating principle and in the seminal vapor; and the nature which is in this spirit corresponds proportionately to the elements composing the stars." Therefore, from a mingling of elements not the intellect only, but not even the vegetative soul is produced.

The difficulty which the third objection proposes, namely, that it would follow that the sensitive and vegetative souls would also have existence from without, by an extrinsic principle, if the intellective soul has, is not relative to the discussion. For it is clear from Aristotle's words that he left it uncertain, whether the intellect differs from the other faculties of the soul both as to subject and as to location, as Plato held, or whether they are only logically distinct [i.e., according to reason]. But if it is granted that they are the same as regards their subject, as is the more probable, then there is no difficulty. For Aristotle says in II De anima: "The cases of figure and soul are exactly parallel." For always, in that which exists with greater complication (consequenter)—whether in geometric figures or in living things—there exists potentially that which is simpler, or prior; just as in a square, a triangle exists in a certain way, and in a sensitive being, that which is vegetative.

That the intellect, in a similar way, exists in the same subject, he leaves in doubt. But it can be said that the vegetative and sensitive soul are in the intellective, just as a triangle and square are in a pentagon. Now, the square is indeed, absolutely speaking, an altogether different figure in species from a triangle, but not from a triangle which is contained potentially within it; just as four sides of a square are not specifically different from the three sides of a triangle which are a part of the same figure, though it is distinct from the triangle, existing independently. And if it would happen that diverse figures would be produced by different agents, a triangle existing independently of a square could have the same producing cause as the square and still have a different species of its own; but the triangle which is in the square would have the same producing cause. Thus, therefore, a vegetative soul existing apart from a sensitive soul is specifically of another kind and has another producing cause. Nevertheless, in the case of a vegetative soul existing in a sensitive soul there is the same producing cause for both sensitive and vegetative. If, therefore, it is said that the vegetative and sensitive souls which are in the intellective have consequently an extrinsic cause, no difficulty ensues. For it is not inconsistent that the effect of a superior agent should have the same power as the effect of a lesser agent, yet, at the same time, possess additional powers of its own. Therefore also the intellective soul, although it has its origin from an extrinsic agent, has the same powers that a vegetative soul and a sensitive soul possess, even though these souls may be caused by interior agents.

Thus, therefore, after a most careful examination of almost every word that Aristotle spoke about the human intellect, it seems that his judgment was this: The human soul is the act of the body, and one of its faculties or powers is the possible intellect.

Now we should consider what opinion the other Peripatetics held on this same subject. Let us, then, first note the words of Themistius in his Commentary on De anima (ed. Barbari, Bk. III, chap. 23): The intellect which we say is in potentia (the possible intellect) is more connatural to the soul, indeed, than is the active. I do not say to the soul in general, but to the human soul alone. Now, just as light makes things potential in vision, and at its coming, endowing these potential objects with colors, causes both sight and colors to be in act, but the same intellect also makes objects that are potentially intelligible to be actually intelligible. And a little later he explains: The operative intellect holds the same relation to that intellect which is in potency as does art to matter. On this account also, understanding is immediate with us whenever we wish. For art is not the possession of the inferior matter, but it exists within the total intellect, which is factive. Thus, if a builder in wood did not exist extrinsic to the wood, his power would penetrate it throughout. So, in fact, it is with the active intellect: supervening the intellect which is potential, it makes one intellect with it.

Shortly afterward he continues: We, therefore, are like that which is in potency; but intellect, like that which is in act. So indeed, as in all things composed of potency and act, this thing will be one thing and that which belongs to it will be another; so I will be one thing, and the existence which is mine will be another. Consequently the intellect is likewise a composite of what is potential and what is active. My existence is from what is in act: since those things which I think of and which I write, the intellect, composed of potency and act, writes. It writes, however, not inasmuch as it is in potency, but as it is active: for thus is operation derived from it. And a little later he says more clearly: An animal, therefore, is one thing, and the existence of an animal is another. The existence of the animal is from the soul of the animal. So also what I am is one thing, and my existence is another. However, my existence is from the soul; yet it is maintained, not from all the soul. For it is not from the sensitive soul, since that was matter for the imagination; nor again, from the imagination; nor again, from the imaginative soul, for that was matter for the potential intellect; nor from the possible intellect, for that was matter for the active intellect. Therefore, from the active intellect alone do I possess my existence. Again, shortly afterward, he adds: And nature, having progressed to this point of perfection ceases.…And so we are active intellect.

Afterward also, rejecting the opinion of certain philosophers, he says that: When, indeed, Aristotle replied that in every nature there is that which is as matter, and that which moves or perfects the matter, he necessarily says that in the soul also these differences exist: what is made to exist as this particular kind of intellect in the soul, and what makes it such in the soul. For he says in the soul there is such an active intellect, and that of the human soul this is the worthiest, most exalted part. . . . From these same words it is proper to confirm that Aristotle thought the active intellect was something which belonged to us, or even was our very selves.

From the foregoing words of Themistius it is therefore evident that he says not only the possible intellect, but also the active intellect are parts of the human soul, and that Aristotle thought this; and moreover, that man is what he is, not by reason of the sensitive soul, as some have falsely said, but by reason of the intellective and more principal part of his soul.

I myself have not seen the books of Theophrastus. But Themistius introduces his words in the Commentary on De anima, quoting him as follows: It is better, however, to set forth the statements of Theophrastus regarding the possible intellect, and that which is active. In regard to the possible intellect, he says: “In what way is the intellect something ‘from without’ and in what way superimposed, yet connatural? And because nature of itself maintains a certain natural kind of existence, namely, that of act and potency in all things, it will completes this same order in higher beings. But it must not be understood that the possible intellect is nothing of itself—for this opinion must be disputed—but that it is a kind of potency, just as in material things. And the active intellect, that from without, must be considered not as an object, but as comprising generation itself.”

Theophrastus asked two questions:

first, how the active intellect is extrinsic to us and yet connatural;

secondly, what is the nature of the possible intellect. He answers the second question by saying that the possible intellect is in potency to all things, not as though it were not existent, but as the senses are in potency to sensible objects. From this he infers the answer to the first question, by saying that the active intellect should not be thought of as extrinsic to the soul, as something added to it accidentally, or as preceding it in time, but as existing from the beginning of generation and as embracing and comprising human nature.

That Alexander also held that the possible intellect is the form of the body, even Averroes admits, although I think he wrongly interprets the words of Alexander, just as he assumed too much from what Themistius said. For Averroes says that Alexander taught that the possible intellect is nothing else than a capacity or readiness which is in human nature for the active intellect and for intelligible objects. This readiness or aptitude he regarded as no thing other than the possible intellect which is in the soul, as related to intelligible objects. Hence he said it was not a power in the body, since this power had no corporeal organ and not as Averroes falsely claimed, because he thought no readiness or apt potency was a bodily power.

Furthermore, that we may pass from the Greeks to the Arabian philosophers, we note, in the first place, that Avicenna evidently considered the intellect a power of the soul, which is the form of the body; for thus he speaks in his book, De anima: "The active intellect, that is, the practical intellect, requires the body and the corporeal powers for all its actions. The contemplative intellect also needs the body and its faculties, but not at all times and in every way; for It is sufficient for itself, through itself. "Moreover, the soul is none of these powers, but it is that which possesses them and, as we will show later, is a solitary substance, per se, which has an aptitude for various actions, some of which are not accomplished or in any way possible except through instruments and through use of them; but others of them have no need of such instruments.

Further, in the First Part, he says: "The human soul is the first perfection of the natural, instrumental body, since to it is attributed the power of deliberate, elective action and, by means of reflection, of arriving at an apprehension of universal ideas." But what he afterward states and proves to be true is: "The human soul also, according as it is proper to it in itself—namely, according to its power of intellect alone—is not related to the body as a form (which is limited to the body) and does not require any organ to be prepared for itself."

In addition, the statement of Algazel may be cited, for he says: "When the mingling of elements has been so well and so perfectly equalized that none fairer or more perfect can be found, then it is apt to receive from the Creator the form of forms, more beautiful than all others, that is, the human soul." But in this soul are two powers: the one is operative, the other is knowing; and this latter he calls the intellect, as is evident in succeeding passages. And afterward by many arguments he proves that the operation of the intellect does not take place through any bodily organ.

This, however, we may omit, not wishing, as it were, merely by the authority of these philosophers to combat the error previously stated, but desiring only to show that not only the Latin philosophers—whose words certain of our opponents do not relish—but both the Greeks and the Arabs held this opinion: namely, that the intellect is a part or power or virtue of the soul, which is the form of the body. Therefore, I wonder from which of the Peripatetics any may boastfully claim to have derived this error; unless, perhaps, it is because those holding it prefer less to be true in their thinking in company with the other Peripatetics, than to err in company with Averroes, who was not so much a Peripatetic as a corrupter of Peripatetic philosophy.

Having shown from the statements of Aristotle and of those following him, that the intellect is a power of the soul, which is the form of the body,—though this power which is called the intellect is not the act of any corporeal organ, because its operation does not involve any bodily operation, as Aristotle says—it is now our purpose to inquire into the reasons why this opinion must be held to be true. And since, according to the teaching of Aristotle, one ought to consider the principle of acts through its acts, it seems that our consideration should begin with that act which is properly the intellect's own—which is, to understand.

In regard to this we can have no more assured definition than that which Aristotle proposes: The soul is the principle by which we live and understand. Therefore it is also the specific form of a certain body. And to this reason he attributes such force that he speaks of it as a demonstration. In the beginning of the chapter he says: "To show what a thing is, one ought to give not only a comprehensive definition, as many do in defining terms, but one ought to show what the inner cause of a thing is, and demonstrate it." Then he gives an example: "Just as demonstration is given of what a tetragon or a square is, through the finding of a median proportional line."

The force of this kind of demonstration seems incontestible, because whoever would wish to turn aside from the road it points out must necessarily fall into inconsistency. Now it is evident that this individual man understands. Never, indeed, would we be inquiring about the intellect unless we possessed intelligence; and when we are carrying on our inquiries about the intellect we do not inquire about any other principle than that one by means of which we understand. Therefore Aristotle says: "I speak, moreover, of the intellect, by which the soul understands." And thus Aristotle concludes: "But if something is the first principle by which we understand, this must be the form of the body." This he says because he had previously made evident that that by which a thing first operates is the form. And this is clear through consideration of action, since each thing operates inasmuch as it is in act. Moreover, each thing is in act through its form; whence it follows that that by which it first acts must be the form.

If, however, one should say that the principle of this act of understanding, a principle that we have called the intellect, is not the form, then it is necessary to explain the way in which the action of this principle is the act of this man. To this problem certain philosophers have offered various explanations. One of these philosophers, Averroes, proposes that the principle of understanding, which he calls the possible intellect, is not the soul or a faculty of the soul, except equivocally; but rather, that it is a certain separated substance, as he has said: The understanding, which belongs to the separated substance, is my understanding or that of another, inasmuch as that possible intellect is united to me or to you through the phantasms which are in me or in you. Thus, he says, the process of understanding comes about. For the intelligible species, which becomes one with the possible intellect since it is its form and its act, has two subjects: one is the phantasm, the other is the possible intellect. Therefore, he says, the possible intellect establishes a continuity with us through its form, the phantasms acting as intermediaries; and thus, while the possible intellect understands, this man understands.

Three reasons, however, show clearly that this doctrine is not true. First because, if this were the case, the union of the intellect with man would not be from the first moment of his generation, as Theophrastus says it is, and as Aristotle implies in II Physic., where he says: The natural term of consideration about forms is for the form, according as man is generated by man and the sun. It is clear, moreover, that the natural term of consideration is the intellect; but, according to the doctrine of Averroes, the intellect is not united to man by reason of his generation, but according to the operation of his senses, inasmuch as he is in act as a sentient being: "For the phantasm is activated by the senses according to their act," as is said in the Third Book of the De anima.

Secondly because this union would not be in relation to any one thing, but according to different things. Now, it is evident that the intelligible species, according as it resides in phantasms, is intelligible potentially. In the possible intellect, however, it is intelligible in act, inasmuch as it has been abstracted from the phantasms. If, therefore, the intelligible species is not the form of the possible intellect, except as abstracted from phantasms, it follows that through the intelligible species there is no conjunction of the intellect with the phantasms, but rather it is separate from these images; unless, perhaps, we should say that the possible intellect is continuous with the phantasms, just as a mirror is united to a man whose reflection happens to be in the mirror. But such a kind of union clearly does not suffice to explain united action. For evidently what is the act of the mirror, namely, to reflect, cannot on this account be attributed to the man reflected; wherefore neither can the action of the possible intellect, according to the type of union proposed, be attributed to this man-for example, to Socrates—in such a way that this man should understand.

Thirdly because, granting that one and the same species, numerically, would be the form of the possible intellect and yet be simultaneously in the phantasm, still, it would not suffice to explain how this man would understand. Evidently, through the intelligible species there is something to be understood, but through the possible intellect man understands that thing; just as also through the sensible species something is perceived, but it is through the sense faculty that one experiences sensation. In like manner a wall on which there is color—the sensible species of which is in act in vision—is seen but does not itself see; but an animal having a visual faculty in which this sensible species is possessed, does see. Now, the proposed conjunction of the possible intellect with a man possessing in his imagination phantasms whose intelligible species reside in the possible intellect, would be like the union of the wall, on which there is color, with the eye, in which the species of its color would reside. Just as the wall, therefore, does not see—but its-color is seen—so it would follow that man would not understand, but the phantasms that are his would be understood by the possible intellect. It is impossible, therefore, to explain, according to the position of Averroes, how any man would understand.

But some philosophers, indeed, seeing that the conclusions reached by Averroes' road could not show how this individual man thinks, have turned aside into another road. They say that the intellect is united to man as a mover; and so, inasmuch as unity is produced by the conjunction of body and. intellect, as by the union of a mover and the thing moved, so the intellect is a part of this man. Hence the operation of the intellect is attributed to the man, just as the operation of the eye, which is to see, is attributed to him. It must be asked, however, of one holding this theory, first of all, what kind of individual this is whom we call Socrates. Is Socrates the intellect alone—that is, the mover (motor)? Or is he moved by that which is the body, and yet animated by a vegetative and sensitive soul? Or is he a composite of both? It seems from their position that the third opinion should be held: namely, that Socrates is a being composed of both.

Let us, therefore, proceed against them through the statement of Aristotle in VIII Metaph., where he says: "Now, when anything has parts, not as an aggregation but as a unified whole, there is in the totality besides the parts something that is distinguished as the cause of unity; as in some bodies the cause of the unity of the being is vitality; in others, the humors, or some other modification of being. "But such a being (as Socrates) is a substance of a unique nature, not after the manner of Ilias, a city composed of parts, but a being of one existence. What is it, therefore, that makes a man one, in virtue of which he is unified and not multiple for example, so that one part of him might be 'animal' and the other 'biped' (although there are some who say that this is the case: that he is truly an animal and truly a biped in such a way that the two are really distinct)? "According to this view, man is not both these things, but they will be, by participation, men—not the attributes, of one man, but of two: the one, animal; the other, biped. And the ensemble will not constitute a man who is one and yet multiple—animal and biped. Hence undoubtedly (because some have been accustomed so to define man and so to teach their hearers) this doctrine does not solve the difficulty. But if, as we have said, this one thing is matter, and that other, form—the one in potency, and the other in act—then the problem no longer seems to exist."

But if you say that Socrates is not an absolutely unified being, but a unity of a sort resulting from the aggregation of mover and moved, many difficulties would result. First of all, because if anything is one in so far as and in the same way as it is being, it would follow that Socrates would not be anything, that he would not be in any species or genus, and that further he would not have any action, since there is no action except that of a being. Consequently we do not say that the sailor’s ability to understand is attributable to the totality comprised by the sailor and his ship, but that understanding belongs to the sailor alone; and in like manner (according to the foregoing supposition) to understand will not be the act of Socrates, but of the intellect alone which makes use of the body of Socrates. For only in that totality which is a unity is the action of a part the action of the whole and if anyone says otherwise, he speaks inaccurately.

And if you say that it is in this manner that the heaven understands, namely, through a mover, such an assumption only provides the matter of further difficulty; for what we know of the human intellect ought to be our means of attaining to knowledge about superior intellects, and not contrariwise.

But if it is said that this individual, that is, Socrates, is a body animated by a vegetative and sensitive soul, as seems to follow according to those who hold that this man is not specifically constituted by his intellect but by a sensitive soul which is in some way ennobled by the influence of the possible intellect, then the intellect will not be related to Socrates except as a mover is related to that which is moved. According to this theory, however, the act of the intellect, which is to understand, can in no way be attributed to Socrates, as is apparent for various reasons:

First because of what the Philosopher says in II Metaph.: "In those things in which there is diversity between some work and the action producing it, the action is in that which is produced, as the act of building is in that which is built, and the act of weaving is in the cloth; and similarly in other things of the same order, the mover is wholly in the thing moved. But in the case of those things in which there is no product apart from the action, the action is in the beings producing the action, as light is in the one who sees, and a reflection is in the mirror which reflects." Thus, therefore, even if it is granted that an intellect is united to Socrates as moving him, this does not prove that understanding is in Socrates, or that he understands; because understanding is an act which is in the intellect alone. Therefore it is also false to say, as they do, that the intellect is not the act of the body, but that man himself understands. For it is not possible that understanding should be attributed to a being that has not an act [form] which is intellectual; because intellection can only be in an intellect, as vision in an eye; wherefore there can be no vision except in one whose act is visual [whose substantial form makes vision possible].

Secondly because the action of a mover is not properly attributed to an instrument or to the being moved; on the contrary, the action of the instrument is attributed to the principal efficient cause. For it is not possible to say that a saw uses or controls the artisan; whereas it is possible to say that the artisan saws, although the work is that of the saw. Now, the proper operation of the intellect is to understand. Therefore, even if it is granted that the act of understanding may be transient, passing over into another so as to move it to understand, it still would not follow that understanding would belong to Socrates, if the intellect were united to him only as a mover.

Thirdly because, in the case of those things whose actions are transient, passing over into another, these actions are attributed in contrary ways to the causes of motion and to the things moved. Accordingly a builder is said to erect a building, but the building is said to be erected. Therefore, if understanding, just as motion, should be transient action, passing over into another, still it could not be said that Socrates understands, inasmuch as intellect is united to him as a mover; but rather, it must be said that intellect understands, and that Socrates is understood; or that intellect, by means of Socrates who has been rendered intelligent, moves Socrates, and thus again, Socrates is moved.

Nevertheless it sometimes happens that the action of an efficient cause passes over into the thing moved: for example, when that which is moved, in virtue of that by which it is moved, initiates movement in another—just as something in which heat has been engendered, engenders heat. Therefore some one might be able to say that, though moved by intellect, man in the act of understanding initiates motion, so that from the very fact that he is moved, he understands. This opinion, however, Aristotle opposes in II De anima, from which we have gleaned the principle of his argument. For, after saying that it is primarily by means of a form that we know and that we possess health, namely, the form of science and the form of health, he adds: "Acts, indeed, appear to be in the patient and in the subject of modification," as Themistius in explaining this says. "For, although science and health are, in a certain way, from others—for example, from a teacher and from a physician—nevertheless, in the patient and in his disposition for modification there reside acts which we have shown to be prior, since they are in them by nature." It is, therefore, the intention of Aristotle—and, moreover, it is evidently true—that when one thing moves another and possesses the action of a mover, there must be in it some act from the mover, who has this sort of act; and this is the principle by which it operates, and it is both its act and form; just is in it from its own enkindling agent.

Granted, therefore, that the intellect may move the soul of Socrates either by illuminating it or in any other way, what results in Socrates from the influence of the intellect is that by which he first understands. Moreover, that by which, primarily, Socrates understands (just as by his senses he experiences sensation), Aristotle proves to be in potency to all things and accordingly to have no natural determination except this: that it is "possible" and therefore with no admixture of anything corporeal, but separate. If it is conceded that some separate intellect moves Socrates, nevertheless it still must be maintained that this possible intellect of which Aristotle speaks is in the soul of Socrates, just as the sense faculties are, which are in potency to all the sensible things that Socrates perceives.

If, however, it is said that this individual man, Socrates, is not a being composed of intellect and animate body, and that he is not merely an animate body, but that he is intellect alone then this will be to state the opinion of Plato who, as Gregory of Nyssa tells us, on account of this difficulty did not wish to consider man as consisting of soul and body, but of a soul using a body, and wearing the body, as it were, as one would a garment. Plotinus also, as Macrobius indicates, held that man was a being of this kind, when he said: "The true man us not he who appears to the eyes, but he by whom the one seen is ruled. Thus, when at death animal life departs from the body, the latter, widowed of its ruler, undergoes dissolution; and this body is what appears mortal in man. The soul. however, which is the true man, is an alien to all conditions of mortality." Now, this same Plotinus, one of the great commentators, is listed among those of Aristotle, as Simplicius states in his commentary, Praedicamentorum.

Moreover, this opinion does not seem to be in conflict with the words of Aristotle. For he says in IX Ethic., "It is the part of a good man to be zealous for the good, even by the grace which is his own. For intellect appears to be a grace possessed by every man." But he does not, indeed, on this account say that man is intellect alone, but that what holds the chief place in man is his intellect. Wherefore he subsequently says: "Just as a city-state, or any other organized society, appears to be the principal one, so does man." And to this he adds: "Every man either is this, intellect, or he is especially this." And in this latter sense, I think, the previously cited words of Themistius and those of Plotinus, just now quoted, were spoken when they said: Man is a soul, or intellect.

That man is not intellect alone, or soul alone, may be proved in many ways:

1. [On the basis of unity.] First, by Gregory of Nyssa himself who, after citing the opinion of Plato, adds: "This statement contains a problem which is difficult, or even without solution. For what kind of unity can a soul 'clothed in a body' be? It cannot be altogether simple while wearing this garment of flesh."

2. [Effects on the body.] Secondly, because Aristotle in VII Metaph. shows that "man" and "a horse" and similar things are not forms alone, but a kind of whole composed of form and matter: a unified, individual being is constituted of prime matter and form, as Socrates. Now, man also is similar to other things that are corporeal, and this Aristotle has proved by the fact that no part of the body can be said to be complete without some part or faculty of the soul; and, after the departure of the soul, one does not speak of an eye or of flesh except equivocally. But this would not be the case if man, or Socrates, were intellect alone, or only a soul.

3. [Relation to the will.] In the third place, it would follow that, since the intellect does not operate except by an act of the will (as is proved in III De anima), this would also be in the power of the will: namely, that a man should retain his body when he wished and abandon it when he wished, which very evidently is false.

Thus therefore it is clear that the intellect is not united to Socrates as a mover only, and that even if this should be so, it could not explain the fact that Socrates understands. Consequently those who wish to defend this position must either confess that they themselves understand nothing and so are disqualified from disputing about anything, or they must admit the truth of what Aristotle concludes: That by which we first understand is the species and the form.

This same conclusion can also be derived from the fact that this individual man is assigned to a certain species; but no species is determined except on the basis of form; therefore that through which this man's species is determined is his form. 4. [Distinction of species.] Any species, moreover, is distinguished by that which is the principal operation proper to that species. But the proper act of man, inasmuch as he is man, is to understand. Through this he differs from other animals; hence Aristotle says that in this operation man's ultimate felicity consists. The principle by which we understand is the intellect, as Aristotle says. Therefore it must be united to the body as its form; not indeed in such a way that the possible intellect itself is the act of any bodily organ, but because it is a power of the soul, which is the act of the physically organized body.

5. [Moral effects,] Furthermore, in view of this false position, the principles of moral philosophy are destroyed. Indeed, whatever is in us [as attributable to us] is withdrawn. Now, nothing is in us as that for which we are accountable except through our willing it; wherefore that which is in our power is called "voluntary." The will, however, is in the intellect, as is clear from the statement of Aristotle in III De anima. It is evident also from the fact that in separate substances there is intellect and will; and likewise because it is in the power of the will to love or hate something in general, just as we hate all thieves as a class, as Aristotle says in his Rhetorica.

If, therefore, the intellect is not anything belonging to this man, or truly one with him, but united to him only through phantasms or as a mover (motor), there will be in man no will of his own, but it will reside in the separate intellect. Consequently this man will not be master of his own acts, nor will any act of his be laudable or blameworthy. But to accept such a view is to destroy the principles of moral philosophy. Since, however, such a thing would be absurd and contrary to human life (for in that case there would be no need to hold councils or to enact laws), it follows that the intellect is united to us in such a way that from it and from us a true unity is constituted. But this cannot come about except in the way that has been stated: namely, that the intellect also is one of the powers of the soul, which is united to us as our form. The conclusion is, therefore, that without any doubt this opinion should be held not only because of the revelation of faith, as they say, but also because to oppose it is to go against philosophical evidence which is clearly apparent.

It is not difficult to refute the reasons that some bring forward in opposition to this doctrine. There are those who maintain that, according to this position, it would follow that the intellect would be a material form and so not stripped of all the character of sensible things, and that consequently whatever is received in the intellect is received individually, as in matter, and not universally. They allege further that, if it is a material form, it is not actually intelligible and so the intellect cannot understand itself, though this is evidently false; for no material form is actually intelligible.

The solution of this difficulty is clear from what has previously been said. We do not say that the human soul is the form of the body according to the possible intellect, which, in the teaching of Aristotle, is not the act of any bodily organ. Therefore it remains true that the soul, as regards the possible intellect, is immaterial, is receptive of immaterial objects, and knows itself. Therefore also, Aristotle uttered these remarkable words about the soul: It is the locus of species—not the entire soul, but the intellect.

If, however, it should be objected that a faculty of the soul cannot be more immaterial than the essence, or more simple, then it may be said that the objection would be very well proposed if the essence of the human soul were a material form, which has no existence of its own, but only the existence of the composite—as is the case with other forms (below the human) which have of themselves neither existence nor operation apart from their communication with matter; and for this reason they are said to be immersed in matter. However, because the human soul by its essence is a form united with matter in such a way that matter does not entirely encompass [or absorb] it,—since the dignity of the form exceeds the capacity of matter—the soul is not hindered from having an operation or a power in which matter is not involved.

Anyone saying this should also consider that, if the intellective principle by which we understand should be essentially separate and distinct from the soul, which is the form of our body, it would be, by its very essence, intelligent and intelligible, and there would be no question of a time when it would understand and of another time when it would not. Nor would it require that it should know through intelligible objects or through acts, but it would have knowledge through its own essence, even as other separated substances. Neither would it be fitting that, to understand, it should have any need of our phantasms. For it is not found in the natural order of things that higher substances, to attain their principal perfection, depend upon inferior substances: so, for example, the heavenly bodies are not formed or fitted for their operations by inferior bodies.

Therefore grave error is contained in the opinion of anyone who says that the intellect is a kind of principle which is separate substantially, and yet that, through species received from phantasms, it is perfected and made intelligent in act.

Thus far we have considered what some maintain: namely, that the intellect is not the soul, which is the form of the body, or a faculty of it, but that it is a separate substance. It remains now to discuss their contention that the possible intellect is one for all men. Now, perhaps, to say this in regard to the active intellect might possess a certain amount of reason, and many philosophers have held this position. For no difficulty would seem to result if many beings were perfected by the one agent: just as by the one sun all the visual potentialities of animals are perfected so that they may actually see; but even this comparison with the active intellect is not in accord with the intention of Aristotle, who thinks that the active intellect is a certain power in the soul; wherefore he compares it to a light. But Plato, judging that there is one separate intellect, compares it to the sun, as Themistius says. For there is one sun, but many rays of light diffused by that sun in order that there may be vision. But, whatever be said in regard to the active intellect, to say that there is one possible intellect for all men cannot be true, for many reasons.

1. If the possible intellect is that by which we understand, then one must say either that this individual intelligent man is intellect, or that intellect formally inheres in him; not, indeed, in such a way as to be the form of the body, but because it is a power of the soul, which is the form of the body. Moreover, if anyone says that this individual man is himself intellect, It follows that this individual man is not distinct from that other individual man, and that all men are one man, not merely by participation in the same species, but after the manner of one individual. But if an intellect is in us formally, as has been said, it follows that for different bodies there are souls that are different. For as man in general is constituted of body and soul, so this man—Callias, for example, or Socrates—is composed of this body and this soul. But if souls are individually distinct, and the possible intellect is that power of the soul by which the soul understands, then it must follow that it is numerically different in every man; for it is impossible to conceive of there being numerically but one such power for things that are diverse. 2. Furthermore, if anyone says that man understands through the possible intellect, as through something that belongs to him as his own, but that it is not a part of him as form, but as mover, then, as has been previously shown, it is not possible according to this position to claim that Socrates himself understands.

But should we grant that Socrates understands because his intellect understands—even though the intellectus be only the mover—then he understands just as a man sees because his eye sees. And, to carry out the comparison, let it be supposed that there is numerically but one eye for all men. It must then be asked whether all men will see as one man, or whether they will see as many. To discover the true answer to this question, we must consider what the relation, on both sides, is between a principal agent and an instrument. Now, if many men make use of numerically one and the same instrument, there will be said to be many operations: as, for example, when many use the one machine to hurl or lift a stone. But if one principal agent employs many instruments, notwithstanding that he who acts is one, the operations may chance to be diverse because of the different instruments used. Sometimes, however, there is but one operation even though many instruments are required for it. Thus, therefore, the unity produced by a worker is determined, not by the instruments, but by the principal agent who uses the instruments.

According to the previously stated position, therefore, if the eye should be the principal thing in man, in such a way that it would use all the powers of the soul and the parts of the body as its instruments, then many, having the one eye, would see as one. But if, on the other hand, the eye is not principal in man, but there is in him something superior that uses the eye as an instrument and that is diversified in different subjects, then there would be many seeing, but only one eye.

However, it is clear that the intellect is that which is principal in man, and that which uses all the powers of the soul as well as all the members of the body; wherefore Aristotle has accurately said: "Man is principally intellect." If, therefore, there should be but one intellect for all men, it would follow necessarily that there would be but one intelligent being and consequently one will and one agent using, according to the dictates of his own will, all those attributes by which men are differentiated from one another. Furthermore, from this fact it would likewise follow that there would be no difference among men as regards free election of the will; but the same things would be done by all if the intellect (in which alone resides the sovereignty and command over all the other powers) is one and the same in different men—a supposition evidently false and impossible. For such a doctrine is in opposition to facts that are clearly apparent. And it likewise would destroy the whole science of morality and all that pertains to the conservation of organized society which, as Aristotle says, is natural to all men.

Furthermore, if all men understood by means of one intellect, no matter in what way it were united to them (whether as form or as mover), it would necessarily follow that there would be numerically but one act of understanding for all men: that is, at one and the same time and in respect to the same intelligible object. For example: if I know a stone and you likewise know it, it must be that one and the same intellectual act is both mine and yours. For there can be numerically, on the part of the same principal active agent (whether that agent is form or mover), only one operation of the same species in respect to the same object at the same time. This fact is clear from what the Philosopher determines in V Physic. Hence, if many men should possess one eye in common, the vision of all could be but one in regard to the same object at the same time.

And similarly, if there be but one intellect for all men, it follows that for all men understanding the same thing at the same time, there is only one in intellectual act; and, more remarkable still, none of those qualities by reason of which men are considered to differ from one another will be changed in the intellectual act. Now, the phantasms are the prerequisites [or predecessors] for the act of intellect, just as colors are for seeing. But, according to this theory, by their diversity the act of intellect is not diversified, especially the act of understanding a single intelligible object. It is by reason of these phantasms, nevertheless, that we judge the knowledge of one man to differ from that of another, inasmuch as the one understands those things that he possesses certain images of, while the other man understands those that he possesses phantasms of. But [according to this theory], in two men who know and understand the same thing, the operation of the intellect cannot be said to be diversified in any way because of different phantasms.

4. Moreover, it can also be shown that this position is evidently at variance with the doctrine of Aristotle. For, after stating that the possible intellect is separate and that it is in potency to all things, he adds: "When it comes to know anything at all, it is in act; just as the one knowing is called the knower, according to the act, this title being derived from the act itself." In this way, science is an act, and the knower is said to be in act inasmuch as he possesses the habit of science. Thereupon Aristotle continues: "This, without doubt, is the case when 'a thing is able to act through itself. It is then still potential, in a certain way, but not in the same way as before learning or discovering something." And, later, when he had inquired, "If the intellect were simple and impassible, having nothing in common with matter, as Anaxagoras said, how, then, could it understand if to understand is said to mean to be passive to something?" To solve this difficulty, he replies: "The intellect is, in a certain way, in potency to intelligible objects, but it is not in act before it actually understands something. It must be, therefore, like a tablet upon which nothing has been written, and this is, indeed, the case in regard to the intellect." Therefore it is Aristotle's opinion that the possible intellect, before it learns or discovers anything, is in potency, as a tablet is upon which nothing has actually been written. But after it has learned and discovered something, by virtue of its aptitude for knowledge—an aptitude or power by which it operates through itself—it is in act, although even then it is in potency to reflect further.

5. Here three things must be noted.

First, this aptitude for knowledge is the first act of the possible intellect itself which, because of it, comes to be in act and is enabled to operate through itself. For knowledge is not only because of the phantasms' being illuminated, as some say, nor is it a certain faculty acquired in us by frequent meditation and exercise so that we may be united with the possible intellect through our phantasms.

Secondly, before our learning or discovering anything, the possible intellect itself is in potency, as a tablet is on which nothing has been written.

Thirdly, by our learning or discovering something the possible intellect is rendered active.

These statements, however, cannot be established as true if there is but one possible intellect for all men who are, who will be, and who have been. Now, evidently the species are preserved or stored, as it were, in the intellect; for it is the locus of the species, as the Philosopher has said above, and as is also evident from the fact that science is a permanent habit. If, then, the intellect of any man has been activated as regards an intelligible species, through the enlightenment given him by a predecessor, and perfected by the habit of science, this acquired habit and the species remain in him. But, since any recipient must be [previously] without that which it receives, I cannot learn and discover what is received in the possible intellect. If, nevertheless, some one says that, by reason of our power of discovery, the possible intellect is rendered active in regard to something for the first time-for example, if I come upon something intelligible, that it is found by reason of no predecessors—still it is not possible to establish this in the matter of learning; for I cannot understand a thing by learning it from another unless he who teaches me knows it. In vain, therefore, has he said that before learning anything the intellect is in potency.

But if any one adds that, according to Aristotle's opinion, men have always existed, it follows that there would have been no first man to understand anything, and so the intelligible species are not acquired by the possible intellect through the phantasms of any man, but are the intelligible species of an eternal possible intellect. In vain, therefore, has Aristotle stated that there is an active intellect which renders those species that are potentially intelligible actually so. In vain has he declared that the phantasms are related to the possible intellect as colors are to vision, if the possible intellect receives nothing from the phantasms. However, it seems to be unreasonable that substances separated from phantasms should receive ours, and that they should be unable to know themselves except after our learning, discovery, or understanding, since Aristotle has added to the foregoing words: "It is also, then, able to know itself either by learning or discovery." For a separated substance has intellection. through itself. Therefore the possible intellect, if it were a separate substance, would know itself through its own essence, and would have no need of those intelligible species that might supervene to it as a result of our intellection or discovery.

6. If, however, our opponents try to avoid this difficulty by saying that Aristotle makes all the foregoing statements in regard to the possible intellect as it exists in a restricted way in us, and not as it is in itself, we may reply that they do not understand the words of Aristotle; for, indeed, what is said is about the possible intellect and what is proper to it, as it is differentiated from the active intellect. But if there is insistence as to Aristotle's words, let us suppose, as our opponents say, that the possible intellect possesses, from all eternity, intelligible species, through which a union is established with us, according as there are phantasms in us. Then it will be necessary to agree that the intelligible species in the possible intellect and the phantasms in us are related in one of three ways,

of which one is: that the intelligible species in the possible intellect are received by the phantasm in us, as the words of Aristotle signify. But this cannot be the situation according to the former position, as has been shown.

The second possible mode is that these species are not received by the phantasms, but that they cast a radiance over the phantasms, illuminating them; just as, for example, certain images (species) in the eye might cast a light upon the colors that are on a wall.

And the third possible mode is that the intelligible species in the possible intellect neither are received by the phantasms nor make any impression upon them.

Now, if the second mode is accepted as true,—namely, that the intelligible species illuminate the phantasms, and that as a result they come to be understood—then the following must be true.

First, that the phantasms are rendered intelligible in act, not by the active intellect, but by the possible intellect and through its own species.

Secondly, that this illuminating of the phantasms could not bring about the rendering of the phantasms actually intelligible, for they become intelligible only through abstraction; but this process would be one of reception rather than of abstraction. And furthermore, since every act of reception is according to the nature of the thing received, the illumination by the intelligible species in the possible intellect of phantasms existing in us will not be in an intelligible mode, but only in a sensible and material way. Consequently, as a result of such illumination, we would not be able to understand anything universally. But if the intelligible species of the possible intellect are neither received by the phantasms nor considered to illuminate them, they will be altogether unrelated and will possess no proportionality at all; and the phantasms will contribute nothing to the act of intellection. But this evidently runs counter to truth. Thus, in view of every conceivable mode of relationship, the possible intellect cannot be one for all men.

It remains now to deal with those objections by which our opponents seek to exclude a plurality of possible intellects. Of these objections, the first is that any form which is multiplied according to division of matter is a material form; wherefore there cannot be a plurality of separated substances in the one species. Hence, if there should be many intellects in many men numerically distinguished by division of matter, it would follow necessarily that the intellect would be a material form; but this is contrary to the statement of Aristotle and to his argument proving that the intellect is separate. If therefore it is separate and is not a material form, it can in no way be multiplied according to multiplication of bodies.

To strengthen this reason, some bring forward still another in saying that God could not create many intellects of the same species in diverse men. They say, indeed, that this implies a contradiction, because to have matter and to be numerically multiplied is opposed to the nature of a separate form. They even proceed beyond this, trying to conclude that a separate form is not numerically one, or an individual thing. However, their error seems to be owing to a matter of vocabulary: for they say a thing is not numerically (numero) one unless it is one of many (de numero). A form that is independent, or free of matter, is not one of many, since it has in itself no cause of plurality; for the cause of number is in matter.

Nor again, is this true: that any number is caused by matter. If this were so, Aristotle would have inquired vainly in regard to the number of separate substances. Moreover, Aristotle also states in V Metaph.: Multitude is divided not only by number, but also by species and genus. Neither is it true that a separate substance is not anything singular or individual; for in that case, it would have no operation, since "act is only of singulars," as the Philosopher says. Wherefore, opposing Plato, he says in VII Metaph.: If the ideas were separate, one idea would not be predicated of many, nor could any of them be defined; just as no other being which is the only one of a species can be defined: for example, the sun and the moon. Matter, indeed, is not the principle of individuation in material things except in so far as it cannot be participated by many individuals, since it is a "first subject," not existing in another; wherefore also, speaking of the ideas, Aristotle says: If the ideas were separate, each would be an individual substance that could not be predicated of many.

Separate substances, therefore, are individual and singular. However, they are not individualized by matter, because they are not so produced as to require to be in another, and consequently do not have to be participated in by many. Hence, if any form is produced to be participated in by another, in such a way that it is the act of certain matter, that form can be individualized and multiplied by reason of its relation to matter. We have shown previously, however, that the intellect is united to the soul, which is the act of the body. In many animate beings there are many souls, and in many souls there are many intellectual powers, which are called "intellects." But it does not follow on this account that an intellect is a material power, as has already been proved.

Someone may object that, if numbers of souls are multiplied according to the numbers of bodies, then, when the bodies have been destroyed, a plurality of souls will no longer exist. The answer to such a difficulty is evident from what has already been stated. For everything is one inasmuch as it is being, as is said in IV Metaph. Thus, although the existence of the soul is in the body, inasmuch as it is the form of the body (nor does it exist before the body), nevertheless, when the body has been destroyed, the soul still remains in possession of its own existence, in such a way that each soul perseveres in its own unity; consequently many souls remain, constituting their own multitude.

Certainly, however, those others who try to prove that God could not create many intellects of the same species, present a clumsy argument, believing that this would involve a contradiction. Now, though we should grant that it is not of the nature of an intellect to be multiplied, we cannot presume that for such an intellect to be multiplied would imply a contradiction. For even though the cause of some quality would not be in the nature of a being, still nothing would prevent its possessing this perfection from some other cause; just as a heavy body has the tendency by its own nature not to be above lighter bodies; nevertheless, for such a heavy body to be thus above does not involve a contradiction; though to be thus above would be, according to its own nature, contradictory. Thus, even if the intellect, by nature, were one for all men because of not having any natural cause for multiplication, still this multiplication could be allotted to it by a supernatural cause: nor would this imply any contradiction. This fact we emphasize, not only in view of the immediate problem, but more in order that the same argument may not be extended to other discussions. For, in the same way, one might be able to conclude that God could not cause the dead to rise, and that sight could not be restored to the blind.

Still another reason is adduced by some in support of their error. For they inquire whether the intellection in me and that in you are altogether and perfectly one, or whether they are two in number and one in species. If one, then there is but one intellect; if numerically two, though one in species, then it will follow that the things intellected will possess the intelligible object. For whatever things are two in number and one in species are understood as one, because there is but one essence by which they are understood; and so one arrives at progression to infinity, which is impossible. Therefore [they say] there cannot be two things numerically intellected—one in me and the other in you. Hence there is but one thing understood, and only one intellect, numerically the same, in all men.

But the question must be asked of those who think that they argue so subtly, whether for two intellects to be numerically distinct, yet one in species, is contrary to the nature of intellect, as intellect, or inasmuch as it is the intellect of man. According to the reason which they advance, it is evident that they mean it is contrary to the intellect as an intellect. For it is according to the nature of the intellect as such, that it should lack nothing that constitutes it as an intellect. Therefore, according to their reasoning, we can conclude absolutely that there is, only one intellect—and not merely one intellect for all men. For if there is only one intellect, then, according to their argument, it follows that there is only one in the whole world, and not simply one for all men. Therefore our intellect is not only a separate substance, but also it is God Himself, and any plurality of separate substances is rendered impossible.

Moreover, if someone should reply that the intellect of one separate substance is not the same in species as the intellect of another separate substance, since the intellects differ specifically, he would merely involve himself in further error: for what is understood is related to the act of understanding and to intellect, as an object is related to act and potency. Now, the object does not receive any species from the act or from the potency, but rather the contrary is true. It must, therefore, be granted absolutely that the intellection of one thing—for example, of a stone—is but one, not only in all men, but even in all intellects.

It now remains to inquire what intellection is. If they say that what is understood is an immaterial species existing in the possible intellect, they unwittingly are going over to the doctrine of Plato, who taught that we cannot have any science of sensible things, but that true science is concerned only with separate form. Nor does it affect the matter whether we say that the science about a stone is possessed in regard to the separate form of a stone, or concerning a form of the stone in the intellect. In each case it follows that science is not concerned with things that are here, but with separate beings only. But because Plato held that immaterial forms of this sort were per se subsistent, he was able also to suppose that many intellects participated in the knowledge of one truth from one separate form. Those, however, who maintain that there are immaterial forms of this sort, which they say are understood, must hold that there is only one intellect, not only for all men, but one absolutely.

Therefore it must be said, according to the opinion of Aristotle, that what is understood, which is one, is the nature itself or the quiddity of the thing. For natural science and the other sciences are of things, not of intelligible species. Now, if what is understood were not the very nature of the stone (which nature is in things), but were the species in the intellect, it would follow that I would not know the thing—that is, the stone—but only the idea abstracted from the stone. But it is also true that the nature of the stone, in so far as it is singular, is potentially intelligible, but becomes actually intelligible by this, that, through the mediation of the senses, the species from sensible things come eventually to the phantasm, and that by the power of the active intellect the intelligible species are abstracted, which are then possessed in the possible intellect. These species, however, are not related to the possible intellect as the objects of its understanding, but as the species by which the intellect knows its object: just as also the species that are in the eye are not the things seen, but those things by which the eye sees—unless so far as the mind reflects upon itself: a thing that cannot occur in a sense faculty.

Furthermore, if understanding were an action passing over into exterior matter, as in the case of burning or moving it, it would follow that intellection would be according to the mode by which a nature really has its existence in singular things (as the action of fire is according to the mode of what is combustible). But because intellection is an action remaining in the person who understands, as Aristotle says in IX Metaph., it follows that understanding is according to the manner of the one knowing, that is, according to the exigency of the species by means of which the intellect understands. These intelligible species, however, since they are abstracted from their individuating principles, do not represent the thing according to any individual conditions, but only according to the universal nature of the thing. Now, if two qualities coexist in an object, nothing hinders one from being capable of representation, even in the senses, without the other; wherefore, the color of honey or of an apple may be seen by the eye without there being any experience of its taste. Thus the intellect understands the universal nature of things by abstracting from individuating principles.

One object, therefore, is understood by me and by you. But it is by means of one thing that it is so understood by me, and by means of another, by you; that is, by a different intelligible species. Thus my intellection is one thing, and yours is another. My intellect is one, and yours is another. Therefore Aristotle says in the Praedicamenta: Every science is individual in relation to its subject. Hence the grammar that a person possesses is said to be in his soul, but is not said to concern the whole person. From this fact, it results also that when my intellect knows that it understands, it knows a certain singular act; but when it understands intellection, absolutely, it knows something universal; for singularity is not repugnant to intelligibility, but materiality is. Therefore, since some singular things are immaterial, such as the separate substances previously discussed, nothing hinders such singulars from being intellected.

Hence it is also apparent how the same science can be in the pupil and in the teacher. The object known is the same, but not the intelligible species by which each understands. Accordingly knowledge in me and in another is individuated; nor is it necessary that the knowledge of a pupil should be caused by the knowledge of the teacher, as is the heat of water by the heat of fire; but as health, which is in matter, by the health which is in the mind of the physician. For just as in the sick man there is a natural principle of health, to which the physician ministers by his skill in order to establish perfect health, so in the pupil there is a natural principle of science, namely, the active intellect, and the first principles, which are intuitively known, per se nota. Moreover, the teacher furnishes certain aids by deducing conclusions from principles known in themselves; and, as the physician strives to produce health according to the manner in which nature heals (by making use of heat and cold), so the teacher develops science in that way by which the pupil may, through his own efforts, come to acquire knowledge: that is, by proceeding from the known to the unknown. And as health is restored to the infirm man, not because of the power of the physician, but because of a faculty of nature, so also knowledge is caused in a pupil, not as something owing to the power of the master, but according to a natural facility for learning.

But there are others who object further that, if many intellectual substances were to remain after the destruction of bodies, it would follow that they would be without any work to perform. So Aristotle in II Metaph. argued that, if there were separate substances that did not animate a body, they would have nothing to do. But if they had well considered this statement of Aristotle, they would have been able easily to solve this difficulty. For before introducing this idea, Aristotle had said previously: "Wherefore it is altogether reasonable to suppose that both these substances and immovable principles exist; but it is left to greater philosophers to declare that they necessarily do so." From this statement it is evident that he himself adhered to the idea that they were probable, and did not declare their necessary existence.

In the second place, since "to be without function or duty occurs when a being does not tend toward the end to which it is ordained, we could not say, even with probability, that the separated substances would be without function if they did not give motion to bodies, unless perhaps we might declare that the moving of bodies is the end for which separate substances exist. But this is quite impossible, since the end must be greater than the beings that are ordained to it. Therefore Aristotle does not say that separate substances would be useless if they did not move bodies, but he says that in his opinion "Every impassible substance, by reason of its very nature, should be assigned to an end supremely good. It is an indication of the greater perfection of anything that it is good not only in itself, but that it causes goodness in others. Consequently, since the way separate substances cause good in lesser beings had not been revealed except through the motion of certain bodies, Aristotle derived from this a probable reason to show that there are no other separate substances than those made known to us by the movement of the heavenly bodies. However, that he did not hold this theory to be necessarily true, he himself declares.

Moreover, we concede that the human soul, after being separated from the body, has not the ultimate perfection of its human nature, since it is a part of human nature. Now, no part is an altogether perfect thing if it has been separated from the whole. Not on this account, however, is the soul without any action; for the end of the human soul is not to animate a body, but to understand; and in this its felicity consists as Aristotle shows in X Ethic.

Still others add a further objection to their assertion of error, saying that if there were as many intellects as there are men it would follow that there would actually be an infinite number, according to the position of Aristotle, who held that the world was eternal and that men had always existed. To this objection, however, Algazel makes answer in his Metaphysics. For he says: "In the case of whatever one of things shall have existed without the other, such as quantity or multitude without order, infinity will not be rendered impossible; even as it is not impossible in the motion of heaven." And later he adds: "Likewise the souls of men, which are separable from bodies at death, we concede to be infinite in number even though they have their existence simultaneously, inasmuch as there is among them no ordination of nature by reason of which some souls should cease to be, since none of them is the cause of the others, but they are altogether equal in nature and in rank, with no priority or posteriority. Now this priority and posteriority are not to be understood as referring to their creation according to time. However, in regard to their essential character, inasmuch as they are essences, there is no order of priority, but they are equal in existence; though they are not as regards time and bodies, and cause and effect."

How Aristotle would have solved this problem, we cannot tell because we do not possess that part of his Metaphysics in which he discussed separate substances. But the Philosopher does say in II Physic. The consideration of forms which are separate or of those which, although they are in matter, are separable from it, is the task of first philosophy. However, no matter what he may have said, evidently on this point Catholics suffer no perplexity; for they hold it [on faith] that the world did have a beginning.

The statement of our opponents, therefore, is evidently false: that it was a principle of all the philosophers, both Arabs and Peripatetics, that the intellect was not numerically multiplied, and that only among the Latin writers was this not held as true. Now, Algazel was not a Latin, but an Arabian. Avicenna also, who likewise was an Arabian, says in his book De anima: "Prudence and stupidity and opinion and other like things do not exist except in the essence of the soul." Hence there is not one soul, but there are numerically many souls; and their species is one.

Furthermore, in order not to omit mention of the Greeks, the words of Themistius regarding this problem are to be noted. In his commentary on the De anima, after he had inquired whether the active intellect were one or many, he proceeds to give his answer: "Can it be truly said that there is but one first intellect illuminating all others, but that there are many which, having received this illumination, subsequently enlighten many others? In the same way, although the sun is only one, the light which goes forth from the sun and is given out by it is, as it were, separated from it and scattered and thus is diffused and distributed in many diverse rays. On this account, Aristotle did not compare the intellect to the sun, but to light; whereas, Plato compared it to the sun." Hence it is evident from the words of Themistius that neither the active intellect of which Aristotle speaks is a single one enlightening all others, nor is that which is illuminated, the possible intellect, only one. But it is true that the principle of all illumination is one: namely, some separate substance: either God, according to Catholic philosophers, or the Ultimate Intellect, according to Avicenna. The unicity of this separate principle, moreover, Themistius proves by the fact that he who teaches and he who learns understand the same thing. This could not be unless there were the same principle of intellectual light for both. But it is true that Themistius afterward relates that certain philosophers had been in doubt whether the possible intellect were one.

He says no more about it, however, because it had not been his purpose to investigate the various opinions of philosophers, but to present the judgments of Aristotle, Plato, and Theophrastus. Therefore at the end he concludes: "But I have stated that to pronounce judgment on what the Philosopher says is a task requiring singular zeal and care. However, this work has had for its purpose to indicate what one can gather from the statements we have collected as to the opinion of Aristotle, of Theophrastus, and more especially, of Plato himself. For the rest, it must be the place and task of another to determine what ought to be believed about the soul. But what the opinion of Aristotle was, and what that of Theophrastus and of Plato, I think can easily be discovered from the quotations from their own books which we have presented and analyzed." Hence it is clear that Aristotle and Theophrastus and Plato himself did not hold it as a principle that the possible intellect is one for all men. It is also evident that Averroes incorrectly presented the opinion of Themistius and of Theophrastus concerning both the possible and the active intellect. Therefore we have rightly called him the perverter of Peripatetic philosophy. Hence it is amazing that certain men, after seeing only the Commentary of Averroes, presume to declare, on his authority, that all the philosophers—Greeks and Arabians, excepting only the Latins—hold this opinion as certain.

However, it is a matter of much greater amazement, or rather even of indignation, that one who professes to be a Christian dares to speak so irreverently in regard to Christian faith. This he does when he says that the Latins do not accept this doctrine among their principles (namely, that there is but one intellect) because perhaps the law of their faith is in contradiction to it. Now, in this there are two evils:

first, because he doubts whether this teaching is against faith;

secondly, because he implies that he himself is estranged from or outside this law, and because he afterward says: "This is the reason why Catholics seem to hold this opinion." Here he calls an article of faith only an "opinion." Nor is it the less presumptuous that later he dares to assert that God could not create many intellects because this implies a contradiction.

However, what he subsequently declares is even more reprehensible: "By reason I conclude of necessity that the intellect is numerically one; nevertheless I firmly hold to the opposite by faith." Therefore he judges that faith is concerned with doctrines the contrary of which can be concluded "of necessity." Since, however, what I conclude of necessity can be only what is necessarily true,—the opposite of which is false and impossible—it follows that faith must be demanded in what is false and impossible: a thing that not even God could do. But the ears of men who have faith cannot endure such words. In his great temerity, moreover, he has not hesitated to dispute about questions that not only do not pertain to philosophy, but that are matters of pure faith: for example, that the soul suffers from the fire of hell, and that the judgment of the doctors on this point should be put aside. With equal reason one might enter into philosophical disputation about the Trinity or the Incarnation and other like questions, concerning which none but a babbler would speak.

These, therefore, are the assembled arguments that we have written in refutation of the aforesaid error, not arguments amassed by reference to the doctrines of faith, but collected from the reasons and words of the philosophers themselves. If any one, however, boastfully claiming a pseudo-science, wishes to say anything in contradiction to what we have written, let him not do his talking in out-of-the-way corners, or before mere boys who know not how to judge of difficult problems. But, if he dares, let him write an answer to what has been here written. He will find not me alone, who am the least, but many others who know and foster the truth, by whom his error may be refuted or his ignorance enlightened.