De unitate intellectus contra Averroistas

Thomas Aquinas

translated as

  1. Aristotle's position on the unity of the possible intellect
  2. The relation of the possible intellect to man, according to other Peripatetics
  3. Reasons in favor of the unity of the intellect
  4. Refutation of the opinion that all men have one intellect
  5. Answer to objections against the multiplicity of intellects


[1] All men by nature desire to know the truth; they also have a natural desire to avoid error and to refute it when the opportunity arises. Since we have been given an intellect in order to know truth and avoid error, it seems singularly inappropriate to be mistaken about it. For a long time now there has been widespread an error concerning intellect which originates in the writings of Averroes. He seeks to maintain that what Aristotle calls the possible, but he infelicitously calls the material, intellect is a substance which, existing separately from the body, is in no way united to it as its form, and furthermore that this possible intellect is one for all men. We have already written much in refutation of this, but because those mistaken on this matter continue impudently to oppose the truth, it is our intention once more to write against this error and in such a way that it is decisively refuted.

[2] There is no need now to show that the foregoing position is erroneous because repugnant to Christian faith: a moment’s reflection makes this clear to anyone. Take away from men diversity of intellect, which alone among the soul’s parts seems incorruptible and immortal, and it follows that nothing of the souls of men would remain after death except a unique intellectual substance, with the result that reward and punishment and their difference disappear. We intend to show that the foregoing position is opposed to the principles of philosophy every bit as much as it is to the teaching of faith. And, Latin writers on this matter not being to the taste of some, who tell us they prefer to follow the words of the Peripatetics, though of them they have seen only the works of Aristotle, the founder of the school, we will first show the foregoing position to be in every way repugnant to his words and judgments.

[3] Let us then take up the first definition of soul Aristotle gives in Book Two of On the Soul (412b5): “the first act of a physically organized body.” And lest some should say this definition does not cover every soul, because of the earlier conditional remark, “If, then, we have to give a general formula applicable to all kinds of soul,” (412b4), which they take to mean that it cannot be done, the words which follow should be taken into account. For he writes, “We have now given a general answer to the question, What is soul? It is substance in the sense which corresponds to the account of a thing.” (412a8-12), that is, the substantial form of a physically organized body.

[4] The sequel answers those who might say that the intellective part is excluded from the range of this definition. “From this it is clear that the soul is inseparable from its, or at any rate that certain parts of it are (if it has parts)—for the actuality of some of them is the actuality of the parts themselves,”(413a4-7), which can only be understood of those which belong to the intellective part, namely intellect and will. From this it is clear that some parts of the soul he has defined as being the act of the body are acts of some parts of the body, whereas others are not the acts of any body. It is one thing for the soul to be the act of body and another for some part of it to be the act of body, as will be argued below. In this same chapter he shows the soul to be the act of body because some of its parts are acts of body: “We must apply what has been said [of the whole] to the parts.”(412b17)

[5] From the sequel it is even clearer that the intellect is covered by this general definition. The fact that the body no longer actually lives when soul is separated from it is taken to be sufficient proof that soul is the act of body. However, because something could be said to be in act thanks to the presence of something other than form, of a mover, say, as the combustible actually burns when fire is present, and the moveable actually moves when the mover is present, one might wonder whether the body actually lives thanks to the presence of soul in the same way that the mobile moves at the presence of the mover, rather than as matter is in act thanks to the presence of form. The doubt can feed on the fact that Plato said soul is united to body not as form but rather as mover and director. This is clear from Plotinus and Gregory of Nyssa—whom I mention because they were Greeks not Latins. The Philosopher invites this doubt when, to what has been quoted, he adds “Further, we have no light on the problem whether the soul may not be the actuality of its body in the sense in which the sailor is the actuality of the ship.”(413a8-10).

[6] It was because this doubt remained after what he said that he concludes, “This must suffice as our sketch or outline of the nature of soul” (413a11-13), because he has not yet shown the truth with full clarity.

Therefore, in order to remove this doubt, he proceeds to make manifest that which is more certain both in itself and in definition through what is less certain in itself but more certain for us, that is, through effects of the soul which are its acts. Thus he immediately distinguishes the works of the soul, saying that “what has soul in it differs from what has not in that the former displays life,”(413a21-25) and that there are many levels of life, namely, “intellect, sense, motion and rest according to place,” the motion of nourishing and growth, such that anything in which one of these is found is said to live. Having shown how these [levels] are interrelated, that is, how one of them might be found without the other, he concludes that the soul is the principle of them all both because the soul “is specified (as by its parts) vegetative, sensitive, intellective and motor,” (413b11-13) and because all these happen to be found in one and the same thing, for example, in man.

[7] Plato held that, insofar as these diverse operations pertain to man, there are diverse souls in him. Consequently he [Aristotle] asks “whether each of these is a soul” by itself or a part of soul, and, if they are parts of one soul, whether they differ in definition alone or also in place, that is, by organ. And, he adds, “of some it is not difficult” to see how it is, but there are others which give rise to doubt. (413b13-26) Consequently, he shows(413b16-21) that in this regard things are clear in vegetable and sensible soul because some plants and animals go on living when divided and all the operations that were in the whole appear in each part. When he adds that “We have no evidence as yet about mind and the power to think,” (413b24-25) he makes clear where the question arises. By saying this he doesn’t mean to show that intellect is not soul, as the Commentator and his followers perversely interpret him, for he clearly says this in response to what was said earlier, “but some present a difficulty” (413b16). This should be understood thus: It is not yet clear whether intellect is a soul or a part of soul, and if it is a part of the soul, whether it is separate in place or in definition only.

[8] Although he says it is not yet clear, nonetheless he indicates what at first blush appears to be the case by adding “It seems to be a widely different kind of soul” (413b25-26). This should not be understood as it perversely is by the Commentator and his followers: namely, that the intellect is equivocally called soul or that the foregoing definition cannot be adapted to it. How it ought to be understood is clear from what he adds, “It alone is capable of existence in isolation from all other psychic powers.” (413b26-27) Therefore it is of another kind in the sense that intellect appears to be something perpetual, whereas the other parts of the soul are corruptible. And because the perpetual and corruptible do not seem to characterize the same substance, apparently only this part of the soul, namely intellect, can be separated, not indeed from body, as the Commentator perversely interprets, but from other parts of the soul, lest they characterize the same substance, soul.

[9] That this is how it should be understood is clear from what he adds, “From these remarks it is clear that the other parts of the soul are not separable” (413b27-28), namely from the substance of the soul or by place. When this was asked earlier the question was resolved from what had just been said. That it is not to be understood as separability from body but as the separability of the powers from one another, is clear from what he adds: “that as understood they are distinguishable by definition,” namely from one another,”is clear,” for to sense and to have an opinion are different.”(413b29-30) Thus what is said here is manifestly in response to the question raised earlier when he asked whether one part of the soul is separated from another in understanding alone or in place. Having set aside this question about intellect, concerning which he determines nothing here, he says it is manifest with respect to the other parts of the soul that they are not separable, that is in place, but that they differ as understood.

[10] It being established therefore that the soul is defined by the vegetative, sensitive, intellective and locomotive parts, he intends to show next that, with respect to each of these, the soul is united to body as form, not as a sailor to his boat. And thus what was previously established only in outline is made certain. He proves this through the operations of the soul in this way: It is manifest that that whereby something first operates is the act of the one operating. For example, we are said to know both through the soul and through science, but first of all through science rather than through the soul—we know through the soul only insofar as it has science; similarly we are said to be healed by the body and by health, but first of all by health. Thus it is clear that science is the form of soul and health of the body.

[11] He continues thus: “The soul is that whereby we first live,” referring to the vegetative, “that whereby we sense” referring to the sensitive, “and move” referring to the locomotive, “and understand,” referring to the intellective. He concludes “It follows that the soul must be an account and essence, not matter or a subject.” (414a12-14) Manifestly therefore he applies here what he said above, that the soul is the act of a physical body, not only to the sensitive, vegetative and motive but also to the intellective. It was Aristotle’s judgment, therefore, that that whereby we understand is the form of the physical body. Should someone say that that with which we understand does not here mean the possible intellect but something else, this is clearly excluded by what Aristotle says in Book Three of On the Soul speaking of the possible intellect: “I call intellect that whereby the soul thinks and understands.” (429a23)

[12] But before we turn to what Aristotle says in Book Three of On the Soul, let us linger on what he has said in Book Two so that his teaching on the soul may become apparent by comparing his statements. For, having defined the soul in general, he begins to distinguish its powers, and says that the powers of the soul are “the vegetative, sensitive, appetitive, locomotive, intellective.” (414a31-32) And that the intellective is the intellect is evident from what he afterwards adds in explanation of the division, “In others, the thinking faculty and intellect, as in men.” (414b18) He holds therefore that the intellect is a power of the soul which is the act of body.

[13] And that he calls the intellect a power of this soul and moreover that the definition of soul given above is common to all the aforesaid parts, is clear from his conclusion: “It is now evident that a single definition can be given of soul in the same way that one can be given of figure. For, as in that case there is no figure apart from triangle and those that follow in order, so here there is no soul apart from the forms of soul just enumerated.” (414b19-22) One ought not then seek any soul apart from those mentioned, to which the definition of soul given above is common. Aristotle makes no further mention of intellect in this second book except when he says that “reasoning and intellect” are “ultimately and rarely” (415a7) because they are in fewer things, as the sequel makes clear.

[14] Because there is a great difference between the ways intellect and imagination operate, he adds that “there is another account of speculative intellect” (415a11-12). This inquiry he reserves to the third book. And lest someone suggest, as Averroes perversely does, that Aristotle speaks of another account of speculative intellect because the intellect is “neither soul nor a part of soul”, this is immediately excluded at the beginning of Book Three where he takes up again the treatment of intellect. For he says, “Concerning the part of the soul whereby the soul knows and understands.” (429a10-11) Nor should anyone think that this is said only insofar as the possible intellect is divided against the agent intellect, as some imagine, for the remark occurs before Aristotle proves there is an agent and possible intellect. Hence he here means by intellect that part in general, insofar as it contains both agent and possible. In much the same way, early in the second book, he manifestly distinguished intellect from the other parts of the soul, as has already been pointed out.

[15] Notice the marvelous care and order of Aristotle’s procedure, beginning Book Three with the treatment of the questions concerning intellect left undetermined in the second. There were two. First, whether intellect is separated from other parts of the soul only as understood or in place too, which indeed he left undetermined when he said, “We have no evidence as yet about thought or the power of reflexion.” (413b24-25) First he takes up this question again when he says “Whether this is separable from the others,” namely from the other parts of the soul, “in definition only, or spatially as well.” (429a11-12) `Spatially separable’ here means the same as `separable in place’ above.

[16] Second, he left unanswered the question concerning intellect’s difference from the other parts of the soul when he said later, “Reflective thought presents a different problem.” (415a11-12) And he immediately begins to inquire into this when he says, “We have to inquire what differentiates this part...” (429a12) He intends to express this difference in such a way that it is compatible with both possibilities mentioned, that is, whether or not it is a soul separable in size or place from the other parts, as this way of speaking sufficiently indicates. For he says we ought to consider what the difference is between the intellect and the other parts of the soul, whether it is separable from them in size or place, that is in subject, or not, or only in understanding. Hence it is clear that he does not intend to give as the difference that it is a substance existing separately from the body, for this would not be compatible with the foregoing; rather, he intends to assign a difference according to the mode of operating. Hence he adds, “...and how thinking takes place.” (429a13) Therefore, from what we can learn from the words of Aristotle up to this point, he clearly held that intellect is a part of the soul which is the act of a physical body.

[17] But because from some words following on these the Averroists wish to take Aristotle’s intention to be that the intellect is not the soul which is the act of the body, or a part of such a soul, we must even more carefully consider what he goes on to say. Immediately after he raised the question about the difference between intellect and sense, he asked in what intellect is like sense and how the two differ. Earlier he established two things about sense, namely that sense is in potency to sensible objects and that sense is affected and corrupted by excessive sensible objects. That is what Aristotle has in mind when he says, “If thinking is like perceiving, it must be either a process in which the soul is acted upon by what is capable of being thought” (429a13-15) in such a way that the intellect would be corrupted by something excessively intelligible as sense is by an excessive sensible object, “or a process different from but analogous to that.” That is, understanding is something similar to sensing, but different in this that it is not affected.

[18] He responds to this question immediately, concluding—not from what went before but from what follows, which however is manifested from what went before—that this part of the soul “must be impassible,”(429a15) in order that it not be corrupted like the senses. There is however another way of being acted upon characteristic of understanding according to which it can be said to suffer in a general sense of the term. In this then it is different from the senses. He goes on to show in what it is like the senses, namely, that this part of the soul must be “capable of receiving the form of the object”(429a15-16) and that it be in potency to this kind of form, not actually being it in its own nature; so too earlier it was said of sense that it is potentially, not actually, sensibles. From this he concludes that “Thought must be related to what is thinkable, as sense is to what is sensible.” (429a16-18)

[19] He brought this out to exclude the opinion of Empedocles (see 404b8-405b30) and other ancients who held that the knower is of the nature of the known, as if we knew earth through earth and water through water. Aristotle showed earlier (417a2-9) that this is not true of sense, because the sensitive power is potentially not actually the things it senses, and he says the same here of intellect.

There is however this difference between sense and intellect that sense is not capable of knowing everything (sight is of colors alone, hearing of sounds, and thus with the others), whereas the intellect is capable of knowing all things whatsoever. Ancient philosophers,(see 405b10-17) thinking that the knower must have the nature of the known, said that in order for the soul to know all things it was necessary that the principles of all things be mingled in it. Aristotle, having proved by analogy with sense that intellect is not actually but potentially what it knows, concludes on the contrary that “intellect, because it knows all things, must be unmixed” (429a18); that is, not composed of all things, as Empedocles held.

[20] In support of this he invokes the testimony of Anaxagoras, (429a19) who is not however speaking of the same intellect, but rather of the intellect that moves all things. It was in order that it might command by moving and separating that Anaxagoras said the latter intellect is unmixed. His subsequent proof of this is found in the Greek text: “For the co-presence of what is alien to its nature is a hindrance and a block” (429a20) This can be understood from what is similar in sight, for if there were some intrinsic color of the pupil, this interior color would prevent an outer color from being seen and in that way would prevent the eye from seeing others.

[21] Similarly, if one of the natures of the things the intellect knows—earth or water, hot or cold, or some such thing—were intrinsic to intellect, that intrinsic nature would impede it and in a way obstruct it from knowing others.

Because it knows all things, therefore, he concludes that “it can have no nature of its own, other than that of having a certain capacity” (429a21-22). That is, its own nature is to be potentially those things it understands; but it actually becomes them when it actually knows them, just as sense in act actually becomes the sensible, as was said above in the second book. Intellect before it actually understands, he therefore concludes, “is not actually any real thing” (429a24), which is the opposite of what the ancients said, namely, that it actually is all things.

[22] Because he mentioned what Anaxagoras said in speaking of the intellect which commands all things, lest he be taken to be saying this of that intellect, he uses this manner of speaking: “That in the soul which is called intellect (by intellect I mean that whereby the soul thinks and judges) is before it thinks, not actually any real thing...” (429a22-24) From which two things are clear: first, that he is not speaking here of an intellect which is a separated substance, but of the intellect he earlier called a power and part of the soul whereby the soul understands; second, that he proved from what was said above that the intellect actually has no a nature.

[23] He has not yet proved, however, that it is not a power in the body, as Averroes says, but immediately concludes this from the foregoing: “For this reason it cannot reasonably be regarded as blended with the body.” (429a25) This second conclusion he derives from the first, which he proved above, namely, that intellect does not actually have any of the natures of sensible things. It follows from this that it is not mixed with body, because if it were mixed with body, it would have some corporeal nature. This is what he adds: “If so, it would acquire some quality, e.g. warmth or cold, or even have an organ like the sensitive faculty.” (429a25-27) Sense is proportioned to its organ and is in a way akin to it in nature, hence with the immutation of the organ the operation of sense too is changed. It is thus then that the phrase, “is not mixed with body,” should be understood: intellect does not have an organ as sense does.

[24] And that the soul’s intellect has no organ he manifests through the saying of those who said that “soul is the place of the forms,” (429a27-29) understanding place broadly for any receiver, in the Platonist manner, except that being the place of forms is not true of the whole soul but only of intellect. For the sensitive part does not receive species in itself, but in the organ; whereas the intellective does not receive them in an organ, but in itself. Again it is not the place of the forms as having them actually, but only in potency.

Since he has now shown what belongs to intellect from its similarity with sense, he returns to what he said first, that “the intellective part must be impassible,” (429a15) and thus with wonderful subtlety concludes from its very similarity to sense its dissimilarity, going on to show that “sense and intellect are not impassible in the same way” (429a29-b5) because sense is destroyed by an excessive sensible but intellect is not destroyed by the excessively intelligible. He gives as reason for this what was proved above: “the reason is that while the faculty of sensation is dependent upon the body, thought is separable from it.”

[25] This is the favorite prop of those who want to hold the error that intellect is neither soul nor part of the soul, but a separated substance. But they too quickly forget what Aristotle said only a little earlier: for just as here he says that “the sensitive is not without body and intellect is separate” so above he said that intellect would “acquire some quality, e.g. warmth or cold, or even have an organ like the senstivie faculty.” (429a25-26) This is the reason, therefore, that he here says that the sensitive is not without body but the intellect is separate: because sense has an organ but intellect does not. Quite obviously, therefore, and without any doubt so far as the text of Aristotle is concerned, it is clear that his view is that possible intellect belongs to the soul which is the act of body, such that the soul’s intellect has no bodily organ as the other powers of the soul certainly have.

[27] It is not difficult to understand how the soul can be the form of a body yet some power of the soul not be a power of body if one takes into account other things as well. For in many things we see that a form is indeed the act of a body of mixed elements and yet has a power which is not the power of any element, but belongs to that form because of a higher principle, namely a celestial body, e.g. the magnet has the power to attract iron and jasper of coagulating blood. And presently we shall see that insofar as forms are nobler they have powers which more and more surpass matter. Hence the ultimate form, the human soul, has a power, namely intellect, which wholly surpasses corporeal matter. Thus the intellect is separate because it isn’t a power in the body but in the soul, and soul is the act of the body.

[28] Nor do we say that the soul, in which the intellect is, so exceeds corporeal matter that it does not exist in the body, but rather that intellect, which Aristotle calls a power of the soul, is not the act of the body. For the soul is not the act of body through the mediation of its powers but is through itself (per se) the act of body, giving to body its specific existence. Some of its powers are acts of certain parts of body, perfecting them for definite operations, but the power which is intellect is not the act of any body, because its operation does not take place by means of a bodily organ.

[29] And lest it seem to anyone that we give this as our own reading, not Aristotle’s meaning, the words of Aristotle expressly stating this must be cited. For in Book Two of the Physics he asks “to what degree it is necessary to know the species and quiddity”, for it is not the natural philosopher’s task to consider every form. And he solves this, adding, “to the degree that the doctor must know sinew and the smith bronze,” that is, up to a point. And up to what point he shows, adding, “until he understands the cause of each,” as if to say, the doctor considers the nerve insofar as it pertains to health, and so too the artisan bronze for the sake of the artifact. And because the natural philosopher considers form insofar as it is in matter, for such is the form of mobile body, so too it should be understood that the naturalist considers form insofar as it is in matter.

[30] The term of the physicist’s consideration of form is of forms which are in some way in matter and in another way not in matter, for these forms are on the border of material and separated forms. Hence he adds, “and concerning these,” namely, those forms which terminate the natural philosopher’s consideration, “which are separable but which do not exist apart from matter...” What these forms are, he goes on to show: “For man is generated by man and by the sun as well.” Man’s form therefore is in matter and separate: in matter indeed insofar as it gives existence to body, for thus it is the term of generation, separate however because of the power which is proper to man, namely intellect. Therefore, It is not impossible for a form to be in matter yet its power be separate, as was shown concerning intellect.

[31] There is yet another way in which they go about showing that Aristotle taught that the intellect is not a soul nor a part of the soul united to body as its form. For Aristotle says in several places that the intellect is perpetual and incorruptible, as is clear in Book Two of the On the Soul (413b26-27), where he says, “...differing as what is eternal from what is perishable; it alone is capable of being separated.” And in Book One where he says that intellect seems to be a substance “incapable of being destroyed” (408b17-18). And in Book Three, he says, “This alone is truly separate and it alone is immortal and perpetual,”(430a22-23) although some do not understand this last to be about the possible intellect, but about the agent intellect. From all these texts it is clear that Aristotle means that intellect is something incorruptible.

[32] However, it seems that nothing incorruptible could be the form of a corruptible body. It is not accidental to form but belongs to it per se that it be in matter, otherwise what comes to be from matter and form would be accidentally one; but nothing can exist without that which belongs to it as such; therefore the form of body cannot be without body. If then the body is corruptible, it follows that the form of body is corruptible. Moreover, forms separate from matter and forms that exist in matter are not of the same kind, as is proved in Book Seven of the Metaphysics. Much less can numerically one form be now in body and now apart from body. With the destruction of the body, therefore, either the form of body is destroyed or it passes to another body. If then intellect is the form of body, it seems necessarily to follow that intellect is corruptible.

[33] It should be known that this argument convinces many: thus Gregory of Nyssa, making the reverse point, understood Aristotle to teach that the soul is corruptible because he made the soul a form. Some maintain because of this that soul passes from body to body. Others held that soul has a certain incorruptible body from which it is never separate. It must be shown, therefore, from Aristotle’s words, that he held that the intellective soul is form and nonetheless held it to be incorruptible.

[34] In Book Eleven of the Metaphysics, after he had shown that forms do not exist before their matters, because “when man is healed then health exists, and the shape of the bronze sphere at the same time as the bronze sphere,” he then asks whether any form remains after matter. In Boethius’s translation, “It should be considered whether anything remains afterward” namely, after matter,”for nothing stands in the way of this in some things, as if the soul were of this kind, not all but intellect, or perhaps it is impossible for them all.” What he clearly says, therefore, is that nothing prevents the soul, which is a form, from remaining after the body thanks to its intellective part although it did not exist prior to body. For when he said absolutely that moving causes are prior but not formal causes, he did not ask whether any form were prior to matter, and he says that nothing prevents this in the case of the form which is soul with respect to its intellective part.

[35] When then, in accordance with the foregoing words of Aristotle, this form which is the soul remains after the body, not the whole but intellect, we must yet ask why the soul remains after the body with respect to its intellective part rather than its other parts, and why other forms don’t remain after their matters. The reason is to be found in the text of Aristotle. He says “This alone is truly separate and this alone immortal and perpetual.”(430a22-23) Thus the reason he gives that it alone seems to be immortal and perpetual is that it alone is separate.

[36] But a question arises as to what he is here speaking of, for some say he means possible intellect and others that he means the agent intellect. But both of these are seen to be false when Aristotle’s words are carefully considered, for Aristotle says both are separate. That it is the whole intellective part which is said to be separate because it has no organ is clear from the words of Aristotle.

[37] In the beginning of On the Soul, Aristotle said that “If there is any way of acting or being acted upon proper to soul, soul will be capable of separate existence.” (403a10-12) The reason for the consequence is this: since anything acts according to the kind of being it is, activity will belong to anything in the same way in which it exists. Forms therefore which have no activity without the participation of their matter, do not themselves operate, but the composite acts through the form. Hence forms of this kind do not themselves exist, but something exists because of them. Heat does not warm, but rather the hot thing; so too heat does not exist properly speaking, but the thing is warm thanks to heat. Because of this Aristotle says in Book Eleven of the Metaphysics that one does not truly say of accidents that they are beings but that they are of beings.

[38] The same reasoning applies to substantial forms having no operation in which matter does not take part, except that such forms are principles of being. Therefore a form which has an activity thanks to one of its powers or faculties in which its matter does not participate has existence of itself. It does not exist simply because its composite does, as is the case with other forms, but rather the composite exists thanks to it. Therefore, the composite being destroyed, a form which exists thanks to the existence of the composite is destroyed, whereas a form through whose existence the composite exists, not vice versa, need not be destroyed when the composite is destroyed.

[39] Against this might be objected what Aristotle says in Book One of On the Soul,”Thinking, loving, and hating are affections not of thought, but of that which has thought, so far as it has it. That is why, when this vehicle decays, memory and love cease; they were activities not of thought, but of the composite which has perished.” (408b25-29) The answer is clear from Themistius who, in explaining this text, says that Aristotle “now is more in the mode of the doubter than the teacher.” For he has not yet destroyed the opinion of those saying that intellect and sense do not differ.

[40] Hence in that whole chapter he speaks of intellect in the same way he does of sense. This is especially evident where he proves the intellect to be incorruptible using the example of sense, which is not corrupted by age. Hence throughout he speaks conditionally and problematically as one inquiring, always conflating intellect and sense. This is chiefly apparent from this that, in the beginning of the solution, he says “We may admit to the full that being pained or please, or thinking, are movements, etc.” (408b5-6) Were anyone adamantly to insist that Aristotle speaks decisively here, another response remains. Understanding is said to be the act of the composite, not essentially but accidentally, insofar as its object, the phantasm, is in a bodily organ and not because this activity is exercised through a bodily organ.

[41] A further question might be asked: If intellect does not understand without the phantasm, how can the soul have an intellectual operation after it is separated from body? The questioner ought to know that it is not the natural philosopher’s task to solve this question. That is why Aristotle, speaking of soul in Book Two of the Physics, writes, “It is the business of First Philosophy to resolve how this is separable and what it is..” For it should be seen that the soul when separated has a different way of understanding than it does when conjoined, a way similar to that of separate substances. Hence it is not surprising that Aristotle should say, in Book Three of On the Soul, “Whether it is possible for it while not existing separate from spatial conditions to think anything that is separate, or not, we must consider later.” (431b17-19) This suggests that it can understand something in a separated state that it cannot when unseparated.

[42] What is especially to be noticed in these words is that, while he said earlier that both intellects, namely the possible and agent, are separate, here he says intellect is not separate. For the separate is such insofar as it is not the act of an organ and the non-separate that which is a part or power of the soul which is the act of body, as has been said. Aristotle’s resolution of such questions can be more certainly gathered from what he wrote of separate substances at the beginning of Book Twelve of the Metaphysics, ten books of which I have seen though they are not yet translated into our language.

[43] Given this, therefore, it is clear that there are no necessary arguments for the opposed position. For it is essential to the soul that it be united to body and this is accidentally impeded, not on its part, but on the part of the body which corrupts. In the same way it pertains as such to what is light that it be above. “This is the essence of what is light that it be above,” as Aristotle says in Book Eight of the Physics, “but it can come about through some impediment that it is not above.”

The response to the second argument is clear from this. Although there is a specific difference between that whose nature it is to be above and that whose nature it is not to be above, yet the thing whose nature it is to be above, although it sometimes is and sometimes is not, due to an impediment, is specifically and numerically the same nature. In much the same way, a form whose nature it is to be united to body is specifically different from one whose nature it is not to be united to body, yet a form specifically and numerically the same can be such that its nature is to be united to body although sometimes it actually is and sometimes it is not because of an impediment.

[44] They seek yet another basis for this error in what Aristotle says in the book On the generation of Animals, namely, “intellect comes only from without and it alone is divine.” But no form which is the act of matter comes to it from without, but is educed from the potency of matter. Therefore the intellect is not the form of body.

They object too that every form of a mixed body is caused by the elements; hence if the intellect were the form of the human body, it would not be caused by something else, but would be caused by the elements.

They further object on this score that it would follow that the vegetative and sensitive too would be from something else, which is contrary to Aristotle. This would be especially true when there is a soul one in substance whose powers are vegetative, sensitive and intellective. But, according to Aristotle, the intellective is from without.

[45] The solution of these difficulties readily appears from the foregoing, for when it is said that every form is educed from the potency of matter, it seems that what this means ought to be understood. For if this is only matter’s first existing in potency to the form, nothing prevents our saying that corporeal matter first exists in potency to the intellective soul. Hence Aristotle says in the book On the Generation of Animals, “For at first all such embryos seem to live the life of a plant. And it is clear that we must be guided by this in speaking of the active and sensitive and rational soul. For all three kinds of soul must be possessed potentially before they are possessed actually.”

[46] Because potency is a correlative of act, a thing must be in potency in the same respect that being actual belongs to it. It has already been shown that those forms which have no activities that do not involve matter are such that composites exist through them and they themselves as it were coexist with composites rather than exist themselves. Hence just as their whole existence is in concretion with matter, so they are said to be totally educed from the potency of matter. The intellective soul, however, since it has an operation without body, does not exist solely in concretion with matter, hence it cannot be said to be educed from matter, but it is rather from an extrinsic principle. And this is obvious from Aristotle’s words: “It remains, then, for the reason alone so to enter and alone to be divine,” and he gives the explanation when he adds, “for no bodily activity has any connexion with its activity.”

[47] I wonder whence comes this second objection, namely, that if the intellective soul were the form of a mixed body it would be caused by the mingling of the elements. No soul is caused by the mingling of elements. Right after the words just quoted we read: “Now it is true that the faculty of all kinds of soul seems to have a connexion with a matter different from and more divine than the so-called elements; but as one soul differs from another in honor and utility, so differs also the nature of the corresponding matter. All have in their semen that which causes it to be productive; I mean what is called a vital heat. This is not fire nor any such force, but it is the breath included in the semen and the foam-like, and the natural principle in the breath, being analogous to the element of the stars.” Therefore not even the vegetable soul, let alone intellect, is produced from the mingling of elements.

[48] The third objection, that it would follow that the sensitive and vegetative too would be from an extrinsic principle, is not relevant. For it is already evident from the words of Aristotle that he leaves indeterminate whether intellect differs from the other parts of the soul in subject and place, as Plato said, or by understanding alone. Even if it were given that they are the same in subject, as is truer, still nothing absurd would follow. For Aristotle says in Book Two of On the Soul, “The cases of figure and soul are exactly parallel; for the particulars subsumed under the common name in both cases—figures and living things—constitute a series, each successive term of which potentially contains its predecessor, e.g.the square the triangle, the sensory power the self-nutritive.” (414b28-32)

[49] If however the intellective too is in the same subject, which he leaves in doubt, it would similarly have to be said that the vegetative and sensitive are in the intellective as triangle and square are in the pentagon. For the square is indeed a figure specifically different from the triangle, but not from the triangle potentially in it, no more than four is from the three which is its part, but only from the three existing apart. And if it should happen that different shapes are produced by different agents, the triangle considered as apart and differing from the square would have a different cause from the square, just as it has another species, but the triangle which is in the square has the same producing cause. Similarly the vegetative existing apart from the sensitive is another species of soul and has a different productive cause, but there is the same productive cause of the sensitive and of the vegetative within the sensitive. If then it is said of the vegetative and sensitive which are in the intellective that they are from the extrinsic cause which produces the intellective, nothing unacceptable follows. For there is nothing absurd about the effect of a higher agent having the power that the effect of a lesser agent has, even more so. Hence the intellective soul, although it is from an external agent, nonetheless has the powers had by the vegetative and sensitive souls which are produced by inferior agents.

[50] So it is that those who carefully consider everything Aristotle has to say of the human intellect see clearly that his teaching was that the human soul is the act of the body and that its part or faculty is the possible intellect.


[51] Now we should consider what the other peripatetics had to say about all this. We will first take up the words of Themistius in his Commentary On the Soul. When he says: “This intellect that we say is in potency is more connatural to the soul,”—he means, than the agent intellect—“I don’t mean to every soul, however, but only to the human. And just as light coming to potential seeing and to colors in potency makes them actual, so when this intellect is in act it not only makes intellect to be in act, but also constitutes potential intelligibles as actual intelligibles.” And a little later: “As art is to matter so is the factive intellect to that which is in potency. That is why we understand when we wish to. For it is not an art exterior to matter, but a power invested in the whole intellect which is making, just as, if the builder did not exist exterior to the wood or the brazier to the bronze, they would be able to penetrate through and through. Thus it is that the intellect in act supervenes on intellect in potency, becoming one with it.”

[52] And, a little later, he concludes, “Therefore we are either the intellect in potency or the intellect in act. And if in everything composed of what is in potency and what is in act, it is one thing and what it is for it to exist is another, then I too and what it is for me to exist differ. And I am an intellect composed of potency and act, but what it is for me to be comes from that which is in act. Wherefore what I think and write, an intellect composed of potency and act writes, but it writes not as in potency but as in act; from it derives its activity.” And a little further on yet more clearly: “Just as animal and what it is for animal to exist differ, the latter being due to the animal’s soul, so too I and what it is for me to exist differ. What it is for me to exist comes from soul but not from every part, not from the sensitive, which is matter to the imaginative, nor indeed from the imaginative, for it is matter to possible intellect, nor from that which is intellect potentially, for it is as matter to the agent intellect. From agent intellect alone, therefore, comes what it is for me to be.” And he adds a little later, “And having progressed to this nature stops, there being nothing more honorable which could serve as subject to it. We are therefore the agent intellect.”

[53] And after rejecting the opinion of some others, he says, “Since Aristotle said that in every nature there is that which is matter and that which moves and perfects matter, he says that these differences must also exist in soul, and that there must be an intellect that becomes all things and another that makes it all things. For he says there is in the soul such an intellect and it is the most noble part of the human intellect.” A bit afterward adding, “This same text confirms that he, Aristotle, thinks that either we are the agent intellect or it is a part of us.”

From the foregoing words of Themistius it is clear that he not only holds that the possible intellect is a part of the human soul, but the agent as well, and he says that Aristotle taught this; and further that man is what he is not because of the sensitive soul, as some falsely said, but from the principal part, the intellective.

[54] I have not seen the books of Theophrastus, but Themistius cites him in his commentary, writing, “However it is better to set forth the sayings of Theophrastus concerning the intellect that is in potency and that which is in act. Of that which is in potency he asks: How could intellect exist from outside and as imposed and yet be connatural? And what is its nature? For it is actually nothing yet everything potentially, just like sense. Nor should this be taken to mean that it itself is not, which is carping, but it is as a kind of potential subject as is found in material things. But this ought not to said to be from without, therefore, or something conjoined, but is included from the first coming into being.” (p. 242, II, 54-62)

[55] So Theophrastus asks two things: first, how is the possible intellect from an extrinsic principle yet connatural to us, and second, what is the nature of the possible intellect. He answers the second question first, saying that it is potentially all things, not indeed existing as nothing, but in the way sense is related to sensibles. His answer to the first question follows from this, that it ought not so to be understood to be from outside as if it were something accidentally conjoined or temporally prior, but is there in the first coming into being, as containing and comprehending human nature.

[56] That Alexander held the possible intellect to be the form of the body, Averroes himself admits, although, as I think, he perversely understands Alexander’s words just as he uses the words of Themistius beyond the meaning they bear. For he claims that Alexander said the possible intellect was precisely the preparation in human nature for agent intellect and intelligibles, he understands this preparation to be nothing other than the soul’s intellective potency to intelligible things. Therefore he said that it is not a power in body because such a power does not have a bodily organ. And not for the reason Averroes attributes to him, that no preparation is a power in body.

[57] To turn from the Greeks to the Arabs, it is clear first of all that Avicenna held intellect to be a power of soul which is the form of body. For he says in his book On the Soul, “The active, that is, practical intellect, needs the body and bodily powers for its own actions, but the contemplative intellect does not always and completely need the body and its powers: for it is sufficient unto itself. None of these is the human soul, but the soul is what has these powers and, as we shall maintain later, is a solitary substance, that is, is in itself, and has aptitude for activities some of which are perfected only through instruments and some use of them, while others do not need instruments in any way.”

Again, in the first part he says that “the human soul is the first perfection of a natural body with organs, insofar as the ability to performs acts of deliberate choice, to discover by inquiry. and to grasp universals are attributed to it.” But it is true that later he says and proves that the human soul, because of that which is proper to it, that is, according to its intellective power, “is not related to body as form nor require that an organ be supplied it.”

[58] Next these words of Algazel should be added: “When the mingling of the elements will have been of a most beautiful and perfect equality, than which nothing more subtle and beautiful can be found, then it became apt to receive from the giver of forms a form more beautiful than other form, which is the soul of man. There are two virtues of this human soul: one operative, the other knowing,” which, as is clear from what follows, means intellect. Afterwards he proves with many arguments that the operation of the intellect does not take place through a bodily organ.

[59] We have set forth these things, not wishing to refute the above mentioned error by the authority of philosophers, but in order to show that not only Latin writers, whose language some do not savor, but also Greeks and Arabs, thought that intellect is a part or power or faculty of the soul which is the form of body. So I wonder from what Peripatetics they boast to have derived this error, unless perhaps they have less desire to think correctly with other Peripatetics than to err with Averroes, who was not a Peripatetic but the perverter of Peripatetic philosophy.


[60] Having shown from the words of Aristotle and those who followed him that the intellect is a potency of the soul which is the form of the body although that potency which is intellect is not the act of any organ, “because its operation is not shared by any bodily operation,” as Aristotle says, we must now inquire by way of arguments what ought to be made of all this. And since, according to the teaching of Aristotle, it is from acts that their principles are known, our consideration must begin with the proper act of intellect, namely, understanding.

[61] Concerning which there is no stronger argument than that given by Aristotle when he argues thus: “The soul is that whereby we first live and understand, therefore it is a certain form and species” of some body. (414a12-14) He relies on this argument, therefore, characterizing it as a demonstration, for in the beginning of the chapter he says, “For it is not enough for a definitive formula to express as most now do the mere fact; it must include and exhibit the ground also.” (413a13-20) By way of example, he says that what a tetragon or square is demonstrated through the discovery of the proportional mean.

[62] The power and irrefutability of this demonstration is clear from the fact that whoever wishes to differ with it necessarily says what is absurd. That this singular man understands is manifest, for we would never ask about intellect unless we understood, nor when we ask about intellect are we asking about anything other than that whereby we understand. Thus Aristotle says, “”I mean the intellect whereby the soul understands,” (429a23) and concludes accordingly that if something is the first principle whereby we understand, it must be the form of the body, because he earlier showed that that whereby we first do anything is the form. And this is clear from argument: anything acts insofar as it is in act; anything is in act through its form; therefore that through which something first acts must be form.

[66] If however you should say that the first principle of the act which is understanding, what we call intellect, is not form, then you must find a way in which the act of this principle can be an action of this man. There are those who have tried in various ways to do this. One of them, Averroes, held that the principle of understanding which is called the possible intellect is not a soul or a part of the soul, except equivocally; rather, it is a separated substance. He said that the separate substance’s understanding is mine or yours insofar as possible intellect is joined to me or you through the phantasms which are in me and you. He says that comes about in this way: the intelligible species which becomes one with the possible intellect as its form and act has two subjects, one those phantasms, the other the possible intellect. Therefore the possible intellect is continuous with us through its form by way of phantasms, and thus when the possible intellect understands, this man understands.

[64] There are three ways of showing that this amounts to nothing. First, because then the union of intellect and man would not come into being when he does, as Theophrastus maintains and Aristotle indicates in Book Two of the Physics where he says that the goal of the naturalist’s consideration of forms is the form according to which man is generated by man and the sun. Intellect is obviously the goal of the naturalist’s consideration, yet, according to what Averroes says, intellect is not united with man from his generation, but through the operation of sense insofar as he is actually sensing: imagination is “a movement resulting from an actual exercise of a power of sense,” as is said in On the Soul. (429a1-2)

[65] Second, because this union would have not one but diverse causes. For clearly the intelligible species as it exists in the phantasm is understood only potentially, but abstracted from phantasms, in the possible intellect, it is actually understood. If then the intelligible species is the form of possible intellect only insofar as it is abstracted from phantasms, it follows that [possible intellect] is not united with phantasms through the intelligible species but rather is separated from them. Unless perhaps it is said that the possible intellect is one with phantasms in the way in which the mirror is one with the man whose image is reflected in the mirror; but such a union manifestly does not suffice for the union of the act. For it is obvious that the act of the mirror, which is to represent, is not on this account attributed to the man. No more could the action of possible intellect on the basis of the foregoing conjunction be attributed to this man Socrates in order that this man might understand.

[66] Third, even granted that numerically one and the same species were the form of the possible intellect and at the same time in phantasms, such a conjunction would not suffice to explain that this man understands. For it is obvious that just as something is sensed through a sensible species but one senses something through the sensitive power, so something is understood through the intelligible species, but one understands something through the intellective power. Hence the wall in which the color is, whose sensible species is actually in sight, is seen, and does not see; it is the animal having the power of sight, in which such a species is, that sees. The aforesaid union of the possible intellect with man, in whom exist the phantasms whose species are in the possible intellect, is like the union of the wall, in which the color is, with sight in which the species of its color is. The wall does not see, but its color is seen; thus it would follow that man does not understand, but his phantasms are understood, by the possible intellect. It is impossible, therefore, on the basis of Averroes’s position, to show that this man understands.

[67] Some, seeing that, on Averroes’s position, it cannot be sustained that this man understands, take another path and say that intellect is united to body as its mover, and thus, insofar as body and intellect become one as mover and moved, the intellect is part of this man, and therefore the operation of intellect is attributed to this man in the same way that the operation of the eye, seeing, is attributed to this man. He who says this must be asked, first, what this singular thing Socrates is. Is he only intellect which is a mover? Or is he what is moved by it—a body animated by vegetative and sensitve soul? Or is he composed of both? So far as his position can be discerned, it appears that he adopts the third possibility, namely, that Socrates is composed of both.

[68] Let us then proceed against them making use of Aristotle’s argument in Book Eight of the Metaphysics, “What then it is that makes man one?” (1045a14) “In the case of all things which have several parts and in which the whole is not, as it were, a mere heap, but the totality is something besides the parts, there is a cause of unity; for as regards material things contact is the cause in some cases, and in others viscocity or some other such quality.” (1045a8-12) “Clearly, then, if people proceed thus in their usual manner of definition and speech, they cannot explain and solve the difficulty. But if, as we say, one element is matter and another is form, and one potentially and the other actually, the question will no longer be thought a difficulty.” (1045a20-25)

[69] But if you should say that Socrates is not some one thing absolutely, but one by the coming together of mover and moved, many incoherencies follow. First, indeed, that since anything is one in the manner in which it exists, it would follow that Socrates is not a being and does not belong in a species or genus; and further, that he would have no action, because only beings act. Hence we do not say that understanding the sailor is the grasp of the whole made up of sailor and boat, but of sailor alone; similarly, understanding would not be Socrates’s activity, but only that of the intellect using the body of Socrates. The action of a part is the action of the whole only when the whole is one being. Anyone who says otherwise speaks improperly.

[70] And if you should say that in this way the heaven understands through its motor, this is to appeal to the more difficult case. We must go by way of the human intellect to grasp the higher intellects, not vice versa.

If it be said that this individual, Socrates, is a body animated by the vegetative and sensitive soul—which seems to follow for those who hold that this man is not placed in a species because of intellect, but because of the sensitive soul ennobled by an illumination or conjunction with possible intellect—then intellect relates to Socrates as mover to moved. But then the action of intellect which is understanding can in no wise be attributed to Socrates. There are many ways in which this consequence is seen to be obvious.

[71] First, because of what the Philosopher says in Book Nine of the Metaphysics, “Where, then, the result is something apart from the exercise, the actuality is in the thing that is being made, e.g. the act of building is in the thing that is being built and that of weaving in the thing that is being woven, and similarly in all other cases, and in general the movement is in the thing that is being moved; but when there is no product apart from the actuality, the actuality is in the agents, e.g. the act of seeing is in the seeing subject and that of theorizing in the theorizing subject.” (1050a30-36) So then, although intellect is said to be united with Socrates as mover, this is of no help in locating understanding in Socrates nor in grounding the claim that Socrates understands, for understanding is an action which is in intellect alone. From this too it is clear that they speak falsely who say that understanding itself, not intellect, is the act of body: there can be no act of understanding that is not the act of intellect, because understanding is in intellect alone just as seeing is in sight alone. Seeing can only belong to that whose act is sight.

[72] Second, because the proper act of the mover is attributed neither to the instrument nor to the moved. On the contrary, the action of the instrument is attributed to the principal mover. It cannot be said that the saw makes the artifact, although the artisan can be said to saw, which is the work of the saw. Understanding is the proper activity of intellect; hence even granting that understanding is an action passing on to another like moving, it does not follow that understanding belongs to Socrates if intellect us united to him only as a mover.

[73] Third, because in those things whose activities are transitive, passing over into other things, actions are attributed in opposite ways to movers and moved. Thanks to building the builder is said to build and the building to be built. If then understanding were a transitive action like motion, it still ought not be said that Socrates understands because intellect is united to him as a mover, but rather that intellect understands and Socrates is understood. Or perhaps that intellect by understanding moves Socrates and Socrates is moved.

[74] Sometimes it happens that the action of the mover passes into the thing moved, as when that which is moved moves because it is moved, e.g. when the heated heats. In this way someone might say that that which is moved by the intellect, which in understanding moves, understands by the very fact that it is moved. Aristotle, from whom we take the principle of this argument, resists this claim in Book Two of On the Soul. For when he said that that whereby we first know or are healed is a form, namely science and health, he adds, “For the activity of that which is capable of originating change seems to take place in that which is changed or altered.” (414a11-12) In explaining this Themistius says, “Although knowledge or health are sometimes from others, as from a a teacher or a physician, nonetheless we have shown that, in things that are from nature, the activity of that which is capable of originating change is in what is changed or altered.” It is Aristotle’s meaning, therefore, and evidently true as well, that when the moved moves and has the action of a mover, there must be in it some act from the mover whereby it performs an action of this kind; it is thanks to this that it primarly acts, and this is its act and form. For example, when something heated heats from the heat which is in it from the heater.

[75] Given that the intellect moves Socrates, whether by illumining or in some other way, then the impression made on Socrates by the intellect is that whereby Socrates primarily understands. However, Aristotle has proved (429a9-b5) that that whereby Socrates primarily understands, as he senses by sense, is potentially all things and for this reason has no determinate nature other than to be possible. Consequently it is not mixed with body but separate. Granting then that there is some separate intellect moving Socrates, it would still be necessary that the possible intellect of which Aristotle speaks is in the soul of Socrates just as sense, which is that whereby Socrates senses and is potentially all sensible things, is.

[76] Should it be said, however, that this individual, Socrates, is neither composed of intellect and an animated body, nor an animated body alone, but only intellect, well, this was the view of Plato who, as Gregory of Nyssa says, “because of this difficulty did not want man to be of body and soul, but to be a soul using and as it were clothed with a body.” But Plotinus, as Macrobius reports, claimed that the soul itself is man, saying, “Therefore the true man is not what is seen, but that which rules what is seen. Thus when at death animation departs from the animal, the body falls widowed from the ruler and it is this which is seen in man and is mortal. Every mark of mortality is alien to the soul which is truly man.” Yet Simplicius, in his commentary on the Categories, numbers Plotinus among the greatest commentators on Aristotle.

[77] This doctrine does not seem far distant from the words of Aristotle, who says in Book Nine of the Nicomachean Ethics, “For it is characteristic of the good man to exert himself for the good, and he does so for his own sake, that is, for the sake of the intellectual element in him.” Of course, he says this, not because man is intellect alone, but because intellect is the chief thing in man. Hence in the sequel he says that “just as the state and every other organized whole seems to be that which is the chief thing in it, so too man,” and adds that “any man either is this, namely intellect, or it especially.” It is in this sense that I appraise Themistius’s words earlier and Plotinus’s now when they say that man is soul or intellect.

[78] That man is not intellect alone nor soul alone is proved in many ways. First, by Gregory of Nyssa who, having mentioned Plato’s view, adds, “This saying is puzzling and difficult: how can the soul be one with its garment? For a tunic and its wearer are not one thing.” Second, because Aristotle in Book Seven of the Metaphysics proves that “man and horse and the like” are not form alone, “but terms which are thus applied to individuals, but universally, are not substance but something composed of this particular formula and this particular matter treated as universal, but when we come to the individual, Socrates is composed of ultimate individual matter; and similarly in all other cases.” The proof of this is that no part of the body can be defined independently of some part of soul and, the soul being gone, flesh and eye are such only equivocally, which would not be the case if Socrates were intellect or soul alone. Third, it would follow that, since intellect moves only through the will, as is proved in Book Three of On the Soul, (433a22) this would be among the things subject to will that man could keep his body or shuffle it off when he wished, which is manifestly false.

[79] It is therefore evident that the intellect is not joined to Socrates as a mover; but, even if it were, it would not advance the claim that Socrates understands. Those who wish to defend this position, therefore, must either admit that they themselves understand nothing and are unworthy participants in the debate, or admit what Aristotle concludes: that that with which we first understand is species and form.

[80] This can also be concluded from the fact that this man is placed in some species. The species is derived from form; therefore that through which this man has a species is form. But each thing has its species from that which is the principle of the proper activity of the species; the proper operation of man as man is understanding: it is in this that he differs from the other animals and that is why Aristotle locates ultimate happiness in this activity. But the principle thanks to which we understand is the intellect, as Aristotle says; therefore it must be united to the body as form, not indeed in such a way that the intellective power is the act of some organ, but because it is a power of the soul which is the act of a physically organized body.

[81] Moreover, the position under discussion would destroy the principles of moral philosophy, for it would take away what is in our power. Something is in our power thanks to will, which is why the voluntary is defined as that which is in our power. But will is in intellect, as is evident from Aristotle in Book Three of On the Soul (432b5) and from the fact that intellect and will are found in separate substances as well as from the fact that something is loved or hated universally. We hate the genus of robbers, as Aristotle says in the Rhetoric.

[82] If then intellect is not something of this man such that it is truly one with him, but is united to him only through phantasms or as a mover, will would not be in man, but in the separated intellect. And thus a man would not have dominion over his acts, nor could anyone be praised or blamed for his acts, which is to destroy the principles of moral philosophy. And since that is absurd and out of keeping with human life—it would be unnecessary to take counsel or to pass laws —it follows that intellect is united to us in such a way that we are truly one with it, which can only be in the way suggested, namely, that it be a power of the soul which is united to us as our form. It follows then that this must be held without any doubt, not because of the revelation of faith, as our opponents say, but because to deny it is go against things manifestly obvious.

[83] It is an easy matter to refute the arguments put forward on behalf of the opposite view. For they say that it follows from their position that intellect is a material form, and is not free of every sensible nature, with the consequence that whatever is received in intellect is received as in matter, individually and not universally. And further that if it is a material form, that it is not understood in act, and thus intellect is incapable of understanding itself, which is manifestly false. No material form is understood in act, but only in potency: it becomes understood in act through abstraction.

The answer is obvious from what has been said earlier. For we do not say that the human soul is the form of body according to the intellective power, which according to Aristotle’s teaching is not the act of any organ. (429a27-28) The soul, with respect to the intellective power, is immaterial and receives immaterially and understands itself. Hence Aristotle significantly says that soul is the place of forms “not the whole soul, but the intellect.” (429a28-29)

[84] If it be objected to this that a power of the soul cannot be more immaterial or simpler than its essence—well, that would be a good argument if the essence of the human soul were the form of matter in such a way that it did not exist of itself but only in dependence on the existence of the composite. Other forms have no existence or operations of themselves without a sharing in matter, and are therefore said to be immersed in matter. The human soul exists in its own right and is to a degree united with a matter that does not wholly capture it—this form is greater in dignity than to be a capacity for matter. Nothing prevents its having some operation or power to which matter does not attain.

[85] Let him who says this consider that if this intellective principle whereby we understand existed separate and distinct from the soul which is the form of our body, it would be of itself understanding and understood and not sometimes understanding, sometimes not. Nor would it need to understand itself by way of intelligibles and acts, but would do so through its own essence like other separated substances and it would not be fitting that it need our phantasms in order to understand. The order of things is not such that higher substances require lower substances for their own principal perfection, no more than celestial bodies are formed or perfected in their operations by lower bodies.

The claim that the intellect is some principle separated in substance and yet is perfected and comes actually to understand through species taken from phantasms is, therefore, improbable in the extreme.


[86] So much for the contention that intellect is not the soul which is the form of our body nor a part of it but some kind of separate substance. There remains to discuss the claim that there is one possible intellect for everybody. There would perhaps be some reason for saying this of agent intellect, and many philosophers do say it, for nothing absurd seems to follow from several things being perfected by one agent, as by one sun the visual powers of all animals are able to see. Although this is not Aristotle’s intention—he holds that the agent intellect is in the soul—he nonetheless compares it to a light, and Plato, holding that the intellect is one separate thing, likened it to the sun, as Themistius tells us, for there is one sun but many lights diffused from it for the sake of seeing. But, however it be with the agent intellect, to say that the possible intellect is one for all men appears impossible in many ways.

[87] First, because if the possible intellect is that whereby we understand, of an individual man who understands it must be said either that he is intellect itself or that intellect formally inheres in him, not indeed in such a way that it be the form of the body but rather a power of the soul which is the form of the body. Should anyone say that the singular man is intellect itself, it would follow that this singular man would not differ from another singular man and that all men are one man, not by sharing in the same species, but as one individual. But if intellect is in us formally, it would follow, as has already been said, that there are different forms of different bodies. For just as man is composed of body and soul, so this man, Callias or Socrates, is composed of this body and this soul. If souls differ, however, and the possible intellect is the power of the soul whereby the soul understands, they must differ numerically, for it is impossible to imagine numerically one power of different things. Should someone say that man understands through possible intellect as by something of his own, which however is not a part of him as a form but rather as a mover, it has already been shown above [79] that on this view it can in no wise be said that Socrates understands.

[88] But let us grant that Socrates understands because the intellect understands although intellect is only a mover, as a man sees because the eye sees. And, to keep to the analogy, let us posit that there is numerically one eye for all men. Now we ask whether all men are one seeing entity or many. To discover the truth of the matter, it should be noted that the first mover differs from the instrument, for if many men use numerically one instrument we say there are many agents, for example, when many use one machine for the throwing of stones or for elevation. If however the chief agent is one, but uses many instruments, there is nonetheless one agent even though many instruments are needed for it, though perhaps a diversity of operations because of the diversity of instruments. Sometimes however there is one operation although many instruments are required for it. The unity of the one acting is read not from the instruments but from the chief agent who uses the instruments.

Thus on the position described earlier, if the eye were what is principal in a man and it would uses all powers of the soul and parts of the body as instruments, many having one eye would be one seeing thing. But if the eye were not what is principal in man, but something higher that uses the eye and is diversified in diverse men, there would indeed be many seeing but with one eye.

[89] But obviously it is intellect that is principal in man and uses all the powers of the soul and bodily members as organs. Hence Aristotle’s careful remark that man is intellect “or especially it.” If then there were one intellect for all, it would necessarily follow that there is only one who understands and consequently only one who wills and of his own free will uses all those things thanks to which men are diverse from one another. From which it follows further that there would be no difference between men as to the free choice of will but it would be the same for all, if indeed intellect, in which resides the principality and dominion of using all the others, is one and undivided in all. But this is clearly false, impossible and repugnant to what is obvious; it destroys the whole of moral science and all those things which pertain to civil interchange, which is natural to man, as Aristotle says.

[90] Again, if all men understand by one intellect, however it be united to them, whether as form or as mover, it necessarily follows that of all men there would be numerically one act of understanding which is both simultaneous and of one intelligible object. For example, if I understand stone and you do likewise, it would be necessary that my intellectual activity and yours be one and the same. The operation of the same active principle, be it form or mover, with respect to the same object at the same time, must be numerically one, as is clear from what the Philosopher says in Book Five of the Physics. So, if there were many men having one eye, the seeing of all with respect to the same object at the same time could only be one.

[91] So too if there were one intellect for all, it would follow that there is but one intellectual operation of all men understanding the same thing at the same time, especially since nothing in terms of which men differ from one another would share in the intellectual operation. For phantasms are preambles to the action of intellect, as colors are to the act of vision, hence the action of intellect would not be diversified because of their differences, especially with regard to one intelligible. They distinguish the knowledge of this one from the knowledge of that one because the one understands those things of which he has phantasms and the other those of which he has phantasms. But when two know and understand the same thing, intellectual activity itself can in no way be diversified by the diversity of phantasms.

[92] Further, it should be pointed out that this position manifestly conflicts with the teaching of Aristotle. For when he says of possible intellect that it is separate and potentially all things, he adds that “When thought has become each thing in the way in which a man who actually knows is said to do so,” that is, in the way that knowledge is an act and the knower is said to be in act insofar as he has the habit, he adds, “this happens when he is now able to exercise the power on his own initiative; its condition is still one of potentiality, but in a different sense from the potentiality which preceded the acquisition of knowledge by learning or discovery.” (429b5-9) Later he asks, “If intellect is simple and impassible and has nothing in common with anything else, as Anaxagoras says, how can it come to think at all if thinking involves a kind of passivity?” (429b23-25) And in reply says, “intellect is in a sense potentially whatever is thinkable, though actually it is nothing until it has thought. What it thinks must be in it just as characters are said to be on a writing-table on which as yet nothing actually stands written: this is exactly what happens with intellect.” (429b30-430a2) It is the teaching of Aristotle, therefore, that the possible intellect is in potency prior to learning or discovery, like a table on which nothing is yet written, but after learning and discovery it is in act by the habit of science, thanks to which it can actuate itself even though it is then in potency to actually considering.

[93] Three things should be noted here. First, that the habit of science is the first act of the possible intellect which, thanks to it, comes to be in act and can operate on its own. Science is not only according to illumined phantasms, as some say, or a faculty which we acquire by frequent meditation and exercise, in order that we might be linked with possible intellect by way of our phantasms. Second, it should be noted that before we learn or discover, the possible intellect itself is in potency as a table on which nothing is written. Third, that through our learning or discovering the possible intellect becomes actual.

[94] None of these things could be if there were only one possible intellect for all who are, were or will be. It is obvious that species are conserved in the intellect, for it is the place of forms, as the Philosopher said above (On the Soul, III, 429127-28); moreover, science is a permanent habit. If then one of the foregoing men becomes actual with respect to some intelligible species and is perfected by the habit of science, that habit and those species remain in him. Since any recipient does not have what it receives, it will be impossible that through my learning or discovering those species be acquired by the possible intellect. For although someone might say that through my discovering the possible intellect can newly come to be in act with respect to something, for example if I should discover some knowable thing never before discovered, yet this could not come about through learning, for I can only learn what the teacher knew. It would therefore be pointless to say that the intellect was in potency prior to learning or discovering.

[95] Were someone to add that, according to the opinion of Aristotle, there have always been men, it would follow that there was never a first man who understood and thus intelligible species are acquired by possible intellect through no one’s phantasms but are intelligible species of an eternal possible intellect. In vain therefore did Aristotle posit an agent intellect to make potentially intelligible things actually intelligible; in vain too did he posit that phantasms are to the possible intellect as colors are to sight, if the possible intellect receives nothing from phantasms. For this too seems irrational that a separated substance should receive from our phantasms and that it cannot understand itself save through our learning or understanding. But Aristotle added to the foregoing, “and it can then understand itself,” (429b9) namely, after learning or discovering.

[96] Should they wish to evade these absurdities by claiming that Aristotle says all those things about the possible intellect insofar as it is made one with us and not as it is in itself, it must first be said that Aristotle’s words do not mean that. Indeed he speaks of the possible intellect in terms of what is proper to it and insofar as it is distinguished from the agent. Then, if no help is forthcoming from Aristotle’s words, let us posit, as they say, that the possible intellect eternally has intelligible species through which it is made one with us according to the phantasms which are in us. It is necessary that the intelligible species which are in the possible intellect and the phantasms that are in us be related in one of three ways. The first is that the intelligible species which are in the possible intellect are taken from the phantasms which are in us, as Aristotle’s words suggest. That this is ruled out by the position under consideration has been shown. The second way is that the species are not taken from phantasms but are shone upon our phantasms, for example, if there were species in the eye shining on the colors which are in the wall. The third way is that the intelligible species are neither received in the possible intellect from the phantasms nor imprint something on the phantasms.

[98] If the second way is taken, namely that the intelligible species illumine the phantasms and in this way are understood, it would follow, first, that the phantasms come to be intelligible in act not through the agent intellect but through the possible intellect and its species. Second, that such an illumination of phantasms could not make phantasms intelligible in act: phantasms do not become intelligible in act except through abstraction; but this would be more like a receiving than an abstracting. Again, since any reception is according to the nature of the receiver, the illumining of the intelligible species which are in the possible intellect will not be of phantasms which are in us in an intelligible mode, but sensibly and materially. Thus we could not understand the universal thanks to this kind of illumination. But if the intelligible species of the possible intellect are neither taken from phantasms nor shone upon them, they will be wholly disparate, having no similarity, and phantasms would have nothing to do with understanding, which flies in the face of the obvious. Thus there is no possible way in which the possible intellect could be one and the same for all men.


[99] Arguments intended to exclude a plurality of possible intellects remain to be dealt with. The first is this: Whatever is multiplied by a division of matter is a material form, which is why substances separate from matter cannot be many members of the same species. If then there were a plurality of intellects in many men who are numerically distinguished from one another by the division of matter, it would necessarily follow that intellect is a material form. But that goes against the words of Aristotle and the argument in which he proves the intellect is separate. If then it is separate it is not a material form and can in no way be multiplied according to the multiplication of bodies.

[100] So attached are they to this argument that they say God could not make many intellects of the same species in diverse men, because, they say, this would imply a contradiction: to have a nature that can be numerically multiplied is other than the nature of separated form. They go beyond this, however, and want to conclude from this that no separate form is numerically one nor an individuated thing. They say this is apparent from the word itself, for only that is numerically one which is one of a number of thingss, but form freed from matter is not one of a number because it does not have within it the cause of number, which is matter.

[101] To begin at the end, they seem not to understand their own words in what was just said. For Aristotle, in Book Four of the Metaphysics, says that “the essence of each thing is one in no merely accidental way” and that “similarly it is from its very nature something that is.” If separated substance is being, therefore, it must be one substance, especially since Aristotle says in Book Eight of the Metaphysics that things which have no matter have no cause of their being or of their being one. In Book Five of the Metaphysics, four kinds of unity are distinguished, namely, numeric, specific, generic and proportional. It cannot be said that any separate substance is one only specifically or generically, since this is not to be one simply speaking. There remains that a separate substance is numerically one. Nor is it said to be numerically one because it is one among numbers—number is not the cause of the one but vice versa—but because in numbering it is not divided: one is that which is undivided.

[102] Nor is it true to say that every number is caused by matter, for then Aristotle would have inquired in vain after the number of separated substances. For Aristotle says in Book Five of the Metaphysics that “many” is said not only numerically but specifically and generically. Nor is it true that separate substance is not singular and individuated, otherwise it would have no operation, since acts belong only to singulars, as the Philosopher says; hence he argues against Plato in Book Seven of the Metaphysics that if the Idea is separate, it will not be predicated of many, nor will it be definable any more than other individuals which are unique in their species, like the sun and moon. Matter is the principle of individuation in material things insofar as matter is not shareable by many, since it is the first subject not existing in another. Hence Aristotle says that if the Idea were separate “it would be something, that is, an individual, which it would be impossible to predicate of many.”

[103] Separate substances, therefore, are individual and singular, but they are individuated not by matter but by this that it is not their nature to exist in another and consequently to be participated in by many. From which it follows that if any form is of a nature to be participated in by something, such that it be the act of some matter, it can be individuated and multiplied by comparison with matter. It has already been shown above that the intellect is a power of the soul which is the act of the body. Therefore in many bodies there are many souls and in many souls there are many intellectual powers, that is, intellects. Nor does it follow from this that the intellect is a material power, as has been shown.

[104] Should anyone object that, if the many souls are multiplied according to bodies, it follows that they will not remain when the bodies have been destroyed, the response is obvious from what has already been said. A thing is one in the way it is a being, as is said in Book Four of the Metaphysics; therefore, for the soul to be is to be in the body as its form, nor is it prior to body, nonetheless it remains in existence after the body is destroyed: thus each soul remains in its unity and consequently many souls in their manyness.

[105] They argue most crudely to show that God cannot bring it about that there should be many intellects, believing this to involve a contradiction. For even granting that it is not of the nature of intellect that it be multiplied, it does not follow from this that the multiplying of intellect involves a contradiction. Nothing prevents a thing’s getting from another something that it is not of its nature to have: it is not of the nature of the heavy to be above, yet for the heavy to be above does not involve a contradiction although for the heavy to be above by its very nature would involve a contradiction. Thus if the intellect were naturally one for all because it had no natural cause of multiplication, multiplication could nonetheless come about through a supernatural cause without involving any contradiction. We say this not because of the present question but lest this form of arguing be extended to other cases, for in this way one could conclude that God cannot bring it about that the dead should rise and the blind have their sight restored to them.

[106] To bolster their error they bring forth another argument. They ask whether what is understood in me and in you is completely one or numerically two but specifically one. If what is understood is one, there will be one intellect. If numerically two but specifically one, it follows that they will have as things understood the thing understood. Wherever there are numerically two but specifically one there is one thing understood, because there is one quiddity through which understanding takes place, and thus to infinity, which is impossible. Therefore it is impossible that there be numerically two things understood in me and you. There is one alone, then, and numerically only one intellect in all.

[107] It ought to be asked by those who consider themselves to argue so subtly whether for things understood to be numerically two but specifically one is contrary to the notion of the understood insofar as it is understood, or insofar as it is understood by man. It is clear from the argument they formulate that it is contrary to the notion of the thing understood. For it is of the notion of the thing understood as such that nothing need be abstracted from it in order that it be understood. Therefore, on the basis of their argument, we can conclude, not just that there is only one thing understood by all men, but that there is simply one thing understood. And if there is but one thing understood, on their reasoning it follows that there is only one intellect in the whole world, not only for men. Therefore not only is our intellect a separate substance, it is also God Himself, and the plurality of separated substances is wholly swept away.

[108] One who sought to respond that the thing understood by one separate substance and that understood by another are not specifically one because the intellects differ specifically, would deceive himself because that which is understood is related to understanding and to intellect as an object to act and potency. The object does not take its species from either the act or the power, but rather the other way around. Therefore it must simply be conceded that the understanding of one thing, say a stone, is one alone not only in all men but also in all intelligences.

[109] But it remains to ask what is the understood itself. For if they say that the thing understood is one immaterial species existing in the intellect, in a way they unwittingly slide into the teaching of Plato who taught that there can be no science of sensible things, but every science is of one separated form. It is not relevant whether someone says that the knowledge of a rock is of one separated form of rock or of one form of rock that is in the intellect. In either case it follows that sciences are not of the things that are here, but only of separated things. Because Plato taught that immaterial forms of this kind are of themselves subsistent, he could maintain along with this that many intellects derive from one separate form knowledge of one truth. But those who posit immaterial forms of this kind—which they call the things understood—in the intellect, have to say that there is only one intellect, not only for all men, but absolutely speaking.

[110] In keeping with the teaching of Aristotle, therefore, it ought to be said that the understood thing which is one is the very nature or quiddity of the thing: natural science and the other sciences are of things, not of understood species. For if the thing understood were not the very nature of rock which is in things, but the species which is in the intellect, it would follow that I do not understand the thing that is a stone, but only the intention which is abstracted from the stone. It is true that the nature of stone as it is in singulars is only potentially understood, but it comes to be actually understood because the species come from sensible things, through the mediation of the senses, to imagination, from which the intelligible species which are in the possible intellect are abstracted by the power of the agent intellect. These species, however, do not relate to possible intellect as what is understood, but as species through which the intellect understands, just as the species which are in sight are not the things seen, but that whereby sight sees, save insofar as the intellect reflects upon itself, which cannot happen in the case of sense.

[111] If however understanding were a transitive action passing into exterior matter, like burning and moving, it would follow that understanding exists in the way the nature of things exists in singulars just as the combustion of fire exists according to the manner of the combustible. But because understanding is an action which remains in the one understanding, as Aristotle says in Book Nine of the Metaphysics, it follows that understanding is according to the mode of the one understanding, that is, according to the demands of the species whereby the understander understands. But this, since it is abstracted from individual principles, does not represent the thing in its individual conditions but only according to the universal nature. If two are conjoined in a thing, nothing prevents one of them being represented in sense without the other: hence the color of honey or of the apple is seen by sight without its taste. Just so the intellect understands the universal nature by abstraction from individual principles.

[112] Therefore there is one thing that is understood by me and you, but it is understood by means of one thing by me and by means of another by you, that is, by different intelligible species, and my understanding differs from yours and my intellect differs from yours. Hence Aristotle in the Categories says that knowledge is singular with respect to its subject, “the individual knowledge of grammar is in a subject, the soul, but is not said of any subject.” Hence when my intellect understands itself to understand, it understands some singular activity; when however it understands understanding simply, it understands something universal. It is not singularity that is repugnant to intelligibility, but materiality; thus, since they are immaterial singulars, as was said of separate substances above, nothing prevents such singulars from being understood.

[113] Thus it is clear how there can be the same science in the learner and teacher. For it is the same with respect to the thing known, but not with respect to the intelligible species whereby each knows—in that respect, science is individuated in me and you. Nor is it necessary that the knowledge which is in the learner be caused by the knowledge that is in the teacher as the heat of water by the heat of fire, but as the health in matter is caused by the health that is in the mind of the physician. Just as in the patient there is a natural principle of health to which the physician supplies aids in order that health might be perfected, so in the learner there is a natural principle of knowledge, namely the agent intellect and the first self-evident principles. The teacher supplies certain aids, deducing conclusions from principles known in themselves. Thus the physician strives to heal in the way nature would heal, namely, by heating and chilling; similarly the master leads to science in the way in which one discovering it for himself would acquire it, proceeding, that is, from the known to the unknown. And just as health in the sick person does not come about by the power of the physician but by the capacity of nature, so too knowledge is not caused in the learner by the power of the master, but by the capacity of the learner.

[114] As to the further objection that if, their bodies having been destroyed, many intellectual substances should remain, it would follow that they are otiose, since Aristotle in Book XI of the Metaphysics argued that if there were separated substances which did not move bodies, they would be otiose. But if one carefully considers the text of Aristotle, the difficulty is easily solved. For Aristotle, before giving this argument, says, “the unmovable substances and principles may reasonably be taken to be just so many; the assertion of necessity must be left to more powerful thinkers.” It is clear from this that he is pursuing a kind of probability and not claiming necessity.

[115] Since that is otiose which does not attain the end for which it is designed, they cannot say even with probability that the separated substances are otiose if they do not move bodies, unless perhaps they mean that the motions of bodies are the ends of separated substances, which is completely impossible, since the end is higher than the things that are for the sake of the end. Nor does Aristotle here conclude that they would be otiose if they did not move bodies, but that “every being and every substance which is immune from change and in virtue of itself has attained to the best must be considered an end.” It is the most perfect state of any thing that it not only is good in itself, but also causes goodness in others. But it was not clear how separated substances would cause goodness in inferior bodies save by the motion of some bodies, hence Aristotle derived from this a probable argument to show that there are as many separate substances as are manifested by the heavenly bodies, although as he himself says this has no claim to necessity.

[116] We concede that the human soul separated from body does not have the ultimate perfection of its nature, since it is a part of human nature: no part has complete perfection if it is separated from its whole. But it is not for this reason frustrated, for the end of the human soul is not to move the body, but to understand, in which its happiness consists, as Aristotle proves in Book Ten of the Ethics.

[117] In advancing their error they also say that if there were many intellects for many men, since intellect is incorruptible, it would follow on Aristotle’s view, since he held the world to be eternal and men to have always existed, that there would be an actual infinity of intellects. Algazel responded to this in his Metaphysics saying that “in anything where there is one of these without the other,” that is, quantity or a multitude without order, “infinity will not be taken from it, as in the case of the movement of the heaven.” And later he adds, “Similarly we grant that human souls, which are separable from the body at death, are infinite in number, although they exist at the same time, since there is no natural ordering among them by the removal of which souls would cease to exist; none of them is the cause of the others, but in nature and position they are simultaneously without prior and posterior. There is no prior and posterior in them according to nature save according to the time of their creation. In their essences insofar as they are essences there is no ordering in any way, but they are equal in existence, unlike spaces and bodies and cause and effect.”

[118] We cannot know what Aristotle’s solution to this might have been because we don’t possess that part of the Metaphysics in which he deals with separated substances. In Book Two of the Physics the Philosopher says that of the forms “the mode of existence of the separable” insofar as they are separable, “it is the business of first philosophy to define.” But it is obvious that whatever he says about this would cause no distress to Catholics, who hold that the world began.

[119] They speak falsehood who say that it was a principle with all those who philosophize, both Arabs and Peripatetics, if not for the Latins, that the intellect is not multiplied numerically. Algazel was an Arab, not a Latin. And Avicenna too, who was an Arab, speaks thus in his book On the Soul, “Prudence, stupidity, opinion can only inhere in the essence of the soul. Therefore the soul is not numerically one but many though of one species.”

[120] And lest we omit the Greeks, we should cite the words of Themistius in his commentary. For when he asked of the agent intellect whether it was one or many, he answered: “Or the first illuminator is one but the illumined and illumining many: for the sun is one, but you will say that light is in some way imparted to sight. For this reason Aristotle proposes light rather than the sun in the comparison, but Plato proposes the sun.” It is clear from these words of Themistius that neither the agent intellect, of which Aristotle speaks, is the one who is illuminator, nor the possible that which is illumined. There is indeed one principle of illumination, namely a certain separated substance which is either God, according to Catholics, or the ultimate intelligence according to Avicenna. Themistius proves the unity of this separate principle by the fact that the teacher and learner understand the same thing, which would not be the case if there were not the same illuminating principle. What he says later, that some doubt whether the possible intellect is one, is certainly true.

[121] But he says no more of this because his intention was not to discuss the diverse opinions of philosophers, but to explicate the teachings of Aristotle, Plato and Theophrastus. Hence at the end he concludes, “What I said to express what seemed to philosophers to be the case is of singular difficulty and concern. From what I have said one can gather the views of Aristotle and Theophrastus, and especially of Plato, about them.” It is evident, therefore, that Aristotle and Theophrastus and Themisitius and Plato himself did not hold as a principle that the possible intellect is one for all. Averroes, it is clear, distorts in reporting it the thought of Themistius and Theophrastus concerning possible and agent intellects, so we rightly said above that he is the perverter of Peripatetic philosophy. How wonderful then that some, consulting only the commentary of Averroes, presume to pronounce that what he says is the common view of all philosophers, Greek and Arab, if not the Latins.

[122] It is yet more wonderful, indeed worthy of indignation, that anyone professing himself to be a Christian should presume to speak so irreverently of the Christian faith as to say that, “The Latins do not accept this as a principle,” namely, that there is only one intellect, “perhaps because their law is contrary to it.” There are two evils in this. First, to doubt whether this is against the faith; second, to give the nod to what is alien to this law. Afterward he said, “This is the reason why Catholics seem to hold their position,” where the judgment of the faith is called a position! Nor is there less presumption in what he dares later to assert, namely that God cannot bring it about that there are many intellects, because this implies a contradiction.

[123] Even more serious is this subsequent remark: “Through reason I conclude necessarily that intellect is numerically one, but I firmly hold the opposite by faith.” Therefore he thinks faith is of things whose contrary can be necessarily concluded; since the only thing that can be necessarily concluded is a necessary truth whose opposite is false and impossible, it follows from this statement that faith is of the false and impossible, which not even God can bring about and the ears of the faithful cannot bear. He does not lack the high temerity to presume to discuss what does not pertain to philosophy but is purely of faith, such that the soul suffers from the fire of hell, and to say that the teaching of the doctors concerning these things should be reprobated. By equal right one could dispute concerning the Trinity, the Incarnation and the like, concerning which he speaks only in ignorance.

[124] This then is what we have written to destroy the error mentioned, using the arguments and teachings of the philosophers themselves, not the documents of faith. If anyone glorying in the name of false science wishes to say anything in reply to what we have written, let him not speak in corners nor to boys who cannot judge of such arduous matters, but reply to this in writing, if he dares. He will find that not only I, who am the least of men, but many others zealous for the truth, will resist his error and correct his ignorance.