belonging to him. Man must therefore derive his species from that which is the principle of this operation. But the species of anything is derived from its form. It follows therefore that the intellectual principle is the proper form of man.
But we must observe that the nobler a form is, the more it rises above corporeal matter, the less it is merged in matter, and the more it excels matter by its power and its operation; hence we find that the form of a mixed body has another operation not caused by its elemental qualities. And the higher we advance in the nobility of forms, the more we find that the power of the form excels the elementary matter; as the vegetative soul excels the form of the metal, and the sensitive soul excels the vegetative soul. Now the human soul is the highest and noblest of forms. Wherefore it excels corporeal matter in its power by the fact that it has an operation and a power in which corporeal matter has no share whatever. This power is called the intellect.
It is well to remark that if anyone holds that the soul is composed of matter and form, it would follow that in no way could the soul be the form of the body. For since the form is an act, and matter is only in potentiality, that which is composed of matter and form cannot be the form of another by virtue of itself as a whole. But if it is a form by virtue of some part of itself, then that part which is the form we call the soul, and that of which it is the form we call the "primary animate," as was said above (Q. 75, A. 5).
Reply Obj. 1: As the Philosopher says (Phys. ii, 2), the ultimate natural form to which the consideration of the natural philosopher is directed is indeed separate; yet it exists in matter. He proves this from the fact that "man and the sun generate man from matter." It is separate indeed according to its intellectual power, because the intellectual power does not belong to a corporeal organ, as the power of seeing is the act of the eye; for understanding is an act which cannot be performed by a corporeal organ, like the act of seeing. But it exists in matter so far as the soul itself, to which this power belongs, is the form of the body, and the term of human generation.
And so the Philosopher says (De Anima iii) that the intellect is separate, because it is not the faculty of a corporeal organ.
From this it is clear how to answer the Second and Third objections: since, in order that man may be able to understand all things by means of his intellect, and that his intellect may understand immaterial things and universals, it is sufficient that the intellectual power be not the act of the body.
Reply Obj. 4: The human soul, by reason of its perfection, is not a form merged in matter, or entirely embraced by matter. Therefore there is nothing to prevent some power thereof not being the act of the body, although the soul is essentially the form of the body.
Reply Obj. 5: The soul communicates that existence in which it subsists to the corporeal matter, out of which and the intellectual soul there results unity of existence; so that the existence of the whole composite is also the existence of the soul. This is not the case with other non-subsistent forms. For this reason the human soul retains its own existence after the dissolution of the body; whereas it is not so with other forms.
Reply Obj. 6: To be united to the body belongs to the soul by reason of itself, as it belongs to a light body by reason of itself to be raised up. And as a light body remains light, when removed from its proper place, retaining meanwhile an aptitude and an inclination for its proper place; so the human soul retains its proper existence when separated from the body, having an aptitude and a natural inclination to be united to the body.
Whether the Intellectual Principle Is Multiplied According to the Number of Bodies?
Objection 1: It would seem that the intellectual principle is not multiplied according to the number of bodies, but that there is one intellect in all men. For an immaterial substance is not multiplied in number within one species. But the human soul is an immaterial substance; since it is not composed of matter and form as was shown above (Q. 75, A. 5). Therefore there are not many human souls in one species. But all men are of one species. Therefore there is but one intellect in all men.
Obj. 2: Further, when the cause is removed, the effect is also removed. Therefore, if human souls were multiplied according to the number of bodies, it follows that the bodies being removed, the number of souls would not remain; but from all the souls there would be but a single remainder. This is heretical; for it would do away with the distinction of rewards and punishments.
Obj. 3: Further, if my intellect is distinct from your intellect, my intellect is an individual, and so is yours; for individuals are things which differ in number but agree in one species. Now whatever is received into anything must be received according to the condition of the receiver. Therefore the species of things would be received individually into my intellect, and also into yours: which is contrary to the nature of the intellect which knows universals.
Obj. 4: Further, the thing understood is in the intellect which understands. If, therefore, my intellect is distinct from yours, what is understood by me must be distinct from what is understood by you; and consequently it will be reckoned as something individual, and be only potentially something understood; so that the common intention will have to be abstracted from both; since from things diverse something intelligible common to them may be abstracted. But this is contrary to the nature of the intellect; for then the intellect would seem not to be distinct from the imagination. It seems, therefore, to follow that there is one intellect in all men.
Obj. 5: Further, when the disciple receives knowledge from the master, it cannot be said that the master's knowledge begets knowledge in the disciple, because then also knowledge would be an active form, such as heat is, which is clearly false. It seems, therefore, that the same individual knowledge which is in the master is communicated to the disciple; which cannot be, unless there is one intellect in both. Seemingly, therefore, the intellect of the disciple and master is but one; and, consequently, the same applies to all men.
Obj. 6: Further, Augustine (De Quant. Animae xxxii) says: "If I were to say that there are many human souls, I should laugh at myself."
But the soul seems to be one chiefly on account of the intellect.
Therefore there is one intellect of all men.
_On the contrary,_ The Philosopher says (Phys. ii, 3) that the relation of universal causes to universals is like the relation of particular causes to individuals. But it is impossible that a soul, one in species, should belong to animals of different species.
Therefore it is impossible that one individual intellectual soul should belong to several individuals.
_I answer that,_ It is absolutely impossible for one intellect to belong to all men. This is clear if, as Plato maintained, man is the intellect itself. For it would follow that Socrates and Plato are one man; and that they are not distinct from each other, except by something outside the essence of each. The distinction between Socrates and Plato would be no other than that of one man with a tunic and another with a cloak; which is quite absurd.
It is likewise clear that this is impossible if, according to the opinion of Aristotle (De Anima ii, 2), it is supposed that the intellect is a part or a power of the soul which is the form of man.
For it is impossible for many distinct individuals to have one form, as it is impossible for them to have one existence, for the form is the principle of existence.
Again, this is clearly impossible, whatever one may hold as to the manner of the union of the intellect to this or that man. For it is manifest that, supposing there is one principal agent, and two instruments, we can say that there is one agent absolutely, but several actions; as when one man touches several things with his two hands, there will be one who touches, but two contacts. If, on the contrary, we suppose one instrument and several principal agents, we might say that there are several agents, but one act; for example, if there be many drawing a ship by means of a rope; there will be many drawing, but one pull. If, however, there is one principal agent, and one instrument, we say that there is one agent and one action, as when the smith strikes with one hammer, there is one striker and one stroke. Now it is clear that no matter how the intellect is united or coupled to this or that man, the intellect has the precedence of all the other things which appertain to man; for the sensitive powers obey the intellect, and are at its service. Therefore, if we suppose two men to have several intellects and one sense--for instance, if two men had one eye--there would be several seers, but one sight. But if there is one intellect, no matter how diverse may be all those things of which the intellect makes use as instruments, in no way is it possible to say that Socrates and Plato are otherwise than one understanding man. And if to this we add that to understand, which is the act of the intellect, is not affected by any organ other than the intellect itself; it will further follow that there is but one agent and one action: that is to say that all men are but one "understander," and have but one act of understanding, in regard, that is, of one intelligible object.
However, it would be possible to distinguish my intellectual action from yours by the distinction of the phantasms--that is to say, were there one phantasm of a stone in me, and another in you--if the phantasm itself, as it is one thing in me and another in you, were a form of the possible intellect; since the same agent according to divers forms produces divers actions; as, according to divers forms of things with regard to the same eye, there are divers visions. But the phantasm itself is not a form of the possible intellect; it is the intelligible species abstracted from the phantasm that is a form. Now in one intellect, from different phantasms of the same species, only one intelligible species is abstracted; as appears in one man, in whom there may be different phantasms of a stone; yet from all of them only one intelligible species of a stone is abstracted; by which the intellect of that one man, by one operation, understands the nature of a stone, notwithstanding the diversity of phantasms. Therefore, if there were one intellect for all men, the diversity of phantasms which are in this one and that one would not cause a diversity of intellectual operation in this man and that man. It follows, therefore, that it is altogether impossible and unreasonable to maintain that there exists one intellect for all men.
Reply Obj. 1: Although the intellectual soul, like an angel, has no matter from which it is produced, yet it is the form of a certain matter; in which it is unlike an angel. Therefore, according to the division of matter, there are many souls of one species; while it is quite impossible for many angels to be of one species.
Reply Obj. 2: Everything has unity in the same way that it has being; consequently we must judge of the multiplicity of a thing as we judge of its being. Now it is clear that the intellectual soul, by virtue of its very being, is united to the body as its form; yet, after the dissolution of the body, the intellectual soul retains its own being.
In like manner the multiplicity of souls is in proportion to the multiplicity of the bodies; yet, after the dissolution of the bodies, the souls retain their multiplied being.
Reply Obj. 3: Individuality of the intelligent being, or of the species whereby it understands, does not exclude the understanding of universals; otherwise, since separate intellects are subsistent substances, and consequently individual, they could not understand universals. But the materiality of the knower, and of the species whereby it knows, impedes the knowledge of the universal. For as every action is according to the mode of the form by which the agent acts, as heating is according to the mode of the heat; so knowledge is according to the mode of the species by which the knower knows.
Now it is clear that common nature becomes distinct and multiplied by reason of the individuating principles which come from the matter.
Therefore if the form, which is the means of knowledge, is material--that is, not abstracted from material conditions--its likeness to the nature of a species or genus will be according to the distinction and multiplication of that nature by means of individuating principles; so that knowledge of the nature of a thing in general will be impossible. But if the species be abstracted from the conditions of individual matter, there will be a likeness of the nature without those things which make it distinct and multiplied; thus there will be knowledge of the universal. Nor does it matter, as to this particular point, whether there be one intellect or many; because, even if there were but one, it would necessarily be an individual intellect, and the species whereby it understands, an individual species.
Reply Obj. 4: Whether the intellect be one or many, what is understood is one; for what is understood is in the intellect, not according to its own nature, but according to its likeness; for "the stone is not in the soul, but its likeness is," as is said, _De Anima_ iii, 8. Yet it is the stone which is understood, not the likeness of the stone; except by a reflection of the intellect on itself: otherwise, the objects of sciences would not be things, but only intelligible species. Now it happens that different things, according to different forms, are likened to the same thing. And since knowledge is begotten according to the assimilation of the knower to the thing known, it follows that the same thing may happen to be known by several knowers; as is apparent in regard to the senses; for several see the same color, according to different likenesses. In the same way several intellects understand one object understood. But there is this difference, according to the opinion of Aristotle, between the sense and the intelligence--that a thing is perceived by the sense according to the disposition which it has outside the soul--that is, in its individuality; whereas the nature of the thing understood is indeed outside the soul, but the mode according to which it exists outside the soul is not the mode according to which it is understood. For the common nature is understood as apart from the individuating principles; whereas such is not its mode of existence outside the soul. But, according to the opinion of Plato, the thing understood exists outside the soul in the same condition as those under which it is understood; for he supposed that the natures of things exist separate from matter.
Reply Obj. 5: One knowledge exists in the disciple and another in the master. How it is caused will be shown later on (Q. 117, A. 1).
Reply Obj. 6: Augustine denies a plurality of souls, that would involve a plurality of species.
Whether Besides the Intellectual Soul There Are in Man Other Souls Essentially Different from One Another?
Objection 1: It would seem that besides the intellectual soul there are in man other souls essentially different from one another, such as the sensitive soul and the nutritive soul. For corruptible and incorruptible are not of the same substance. But the intellectual soul is incorruptible; whereas the other souls, as the sensitive and the nutritive, are corruptible, as was shown above (Q. 75, A. 6).
Therefore in man the essence of the intellectual soul, the sensitive soul, and the nutritive soul, cannot be the same.
Obj. 2: Further, if it be said that the sensitive soul in man is incorruptible; on the contrary, "corruptible and incorruptible differ generically," says the Philosopher, _Metaph._ x (Did. ix, 10). But the sensitive soul in the horse, the lion, and other brute animals, is corruptible. If, therefore, in man it be incorruptible, the sensitive soul in man and brute animals will not be of the same genus. Now an animal is so called from its having a sensitive soul; and, therefore, "animal" will not be one genus common to man and other animals, which is absurd.
Obj. 3: Further, the Philosopher says, _Metaph._ viii (Did. vii, 2), that the genus is taken from the matter, and difference from the form. But "rational," which is the difference constituting man, is taken from the intellectual soul; while he is called "animal" by reason of his having a body animated by a sensitive soul. Therefore the intellectual soul may be compared to the body animated by a sensitive soul, as form to matter. Therefore in man the intellectual soul is not essentially the same as the sensitive soul, but presupposes it as a material subject.
_On the contrary,_ It is said in the book _De Ecclesiasticis Dogmatibus_ xv: "Nor do we say that there are two souls in one man, as James and other Syrians write; one, animal, by which the body is animated, and which is mingled with the blood; the other, spiritual, which obeys the reason; but we say that it is one and the same soul in man, that both gives life to the body by being united to it, and orders itself by its own reasoning."
_I answer that,_ Plato held that there were several souls in one body, distinct even as to organs, to which souls he referred the different vital actions, saying that the nutritive power is in the liver, the concupiscible in the heart, and the power of knowledge in the brain.
Which opinion is rejected by Aristotle (De Anima ii, 2), with regard to those parts of the soul which use corporeal organs; for this reason, that in those animals which continue to live when they have been divided in each part are observed the operations of the soul, as sense and appetite. Now this would not be the case if the various principles of the soul's operations were essentially different, and distributed in the various parts of the body. But with regard to the intellectual part, he seems to leave it in doubt whether it be "only logically" distinct from the other parts of the soul, "or also locally."
The opinion of Plato might be maintained if, as he held, the soul was supposed to be united to the body, not as its form, but as its motor.
For it involves nothing unreasonable that the same movable thing be moved by several motors; and still less if it be moved according to its various parts. If we suppose, however, that the soul is united to the body as its form, it is quite impossible for several essentially different souls to be in one body. This can be made clear by three different reasons.
In the first place, an animal would not be absolutely one, in which there were several souls. For nothing is absolutely one except by one form, by which a thing has existence: because a thing has from the same source both existence and unity; and therefore things which are denominated by various forms are not absolutely one; as, for instance, "a white man." If, therefore, man were _living_ by one form, the vegetative soul, and _animal_ by another form, the sensitive soul, and _man_ by another form, the intellectual soul, it would follow that man is not absolutely one. Thus Aristotle argues, _Metaph._ viii (Did. vii, 6), against Plato, that if the idea of an animal is distinct from the idea of a biped, then a biped animal is not absolutely one. For this reason, against those who hold that there are several souls in the body, he asks (De Anima i, 5), "what contains them?"--that is, what makes them one? It cannot be said that they are united by the one body; because rather does the soul contain the body and make it one, than the reverse.
Secondly, this is proved to be impossible by the manner in which one thing is predicated of another. Those things which are derived from various forms are predicated of one another, either accidentally, (if the forms are not ordered to one another, as when we say that something white is sweet), or essentially, in the second manner of essential predication, (if the forms are ordered one to another, the subject belonging to the definition of the predicate; as a surface is presupposed to color; so that if we say that a body with a surface is colored, we have the second manner of essential predication.)
Therefore, if we have one form by which a thing is an animal, and another form by which it is a man, it follows either that one of these two things could not be predicated of the other, except accidentally, supposing these two forms not to be ordered to one another--or that one would be predicated of the other according to the second manner of essential predication, if one soul be presupposed to the other. But both of these consequences are clearly false: because "animal" is predicated of man essentially and not accidentally; and man is not part of the definition of an animal, but the other way about.
Therefore of necessity by the same form a thing is animal and man; otherwise man would not really be the thing which is an animal, so that animal can be essentially predicated of man.
Thirdly, this is shown to be impossible by the fact that when one operation of the soul is intense it impedes another, which could never be the case unless the principle of action were essentially one.
We must therefore conclude that in man the sensitive soul, the intellectual soul, and the nutritive soul are numerically one soul.
This can easily be explained, if we consider the differences of species and forms. For we observe that the species and forms of things differ from one another, as the perfect and imperfect; as in the order of things, the animate are more perfect than the inanimate, and animals more perfect than plants, and man than brute animals; and in each of these genera there are various degrees. For this reason Aristotle, _Metaph._ viii (Did. vii, 3), compares the species of things to numbers, which differ in species by the addition or subtraction of unity. And (De Anima ii, 3) he compares the various souls to the species of figures, one of which contains another; as a pentagon contains and exceeds a tetragon. Thus the intellectual soul contains virtually whatever belongs to the sensitive soul of brute animals, and to the nutritive souls of plants. Therefore, as a surface which is of a pentagonal shape, is not tetragonal by one shape, and pentagonal by another--since a tetragonal shape would be superfluous as contained in the pentagonal--so neither is Socrates a man by one soul, and animal by another; but by one and the same soul he is both animal and man.
Reply Obj. 1: The sensitive soul is incorruptible, not by reason of its being sensitive, but by reason of its being intellectual. When, therefore, a soul is sensitive only, it is corruptible; but when with sensibility it has also intellectuality, it is incorruptible. For although sensibility does not give incorruptibility, yet it cannot deprive intellectuality of its incorruptibility.
Reply Obj. 2: Not forms, but composites, are classified either generically or specifically. Now man is corruptible like other animals. And so the difference of corruptible and incorruptible which is on the part of the forms does not involve a generic difference between man and the other animals.
Reply Obj. 3: The embryo has first of all a soul which is merely sensitive, and when this is removed, it is supplanted by a more perfect soul, which is both sensitive and intellectual: as will be Reply Obj. 4: We must not consider the diversity of natural things as proceeding from the various logical notions or intentions, which flow from our manner of understanding, because reason can apprehend one and the same thing in various ways. Therefore since, as we have said, the intellectual soul contains virtually what belongs to the sensitive soul, and something more, reason can consider separately what belongs to the power of the sensitive soul, as something imperfect and material. And because it observes that this is something common to man and to other animals, it forms thence the notion of the genus; while that wherein the intellectual soul exceeds the sensitive soul, it takes as formal and perfecting; thence it gathers the "difference" of man.
Whether in Man There Is Another Form Besides the Intellectual Soul?
Objection 1: It would seem that in man there is another form besides the intellectual soul. For the Philosopher says (De Anima ii, 1), that "the soul is the act of a physical body which has life potentially."
Therefore the soul is to the body as a form of matter. But the body has a substantial form by which it is a body. Therefore some other substantial form in the body precedes the soul.
Obj. 2: Further, man moves himself as every animal does. Now everything that moves itself is divided into two parts, of which one moves, and the other is moved, as the Philosopher proves (Phys. viii, 5). But the part which moves is the soul. Therefore the other part must be such that it can be moved. But primary matter cannot be moved (Phys. v, 1), since it is a being only potentially; indeed everything that is moved is a body. Therefore in man and in every animal there must be another substantial form, by which the body is constituted.
Obj. 3: Further, the order of forms depends on their relation to primary matter; for "before" and "after" apply by comparison to some beginning. Therefore if there were not in man some other substantial form besides the rational soul, and if this were to inhere immediately to primary matter; it would follow that it ranks among the most imperfect forms which inhere to matter immediately.
Obj. 4: Further, the human body is a mixed body. Now mingling does not result from matter alone; for then we should have mere corruption. Therefore the forms of the elements must remain in a mixed body; and these are substantial forms. Therefore in the human body there are other substantial forms besides the intellectual soul.
_On the contrary,_ Of one thing there is but one substantial being.
But the substantial form gives substantial being. Therefore of one thing there is but one substantial form. But the soul is the substantial form of man. Therefore it is impossible for there to be in man another substantial form besides the intellectual soul.
_I answer that,_ If we suppose that the intellectual soul is not united to the body as its form, but only as its motor, as the Platonists maintain, it would necessarily follow that in man there is another substantial form, by which the body is established in its being as movable by the soul. If, however, the intellectual soul be united to the body as its substantial form, as we have said above (A. 1), it is impossible for another substantial form besides the intellectual soul to be found in man.
In order to make this evident, we must consider that the substantial form differs from the accidental form in this, that the accidental form does not make a thing to be "simply," but to be "such," as heat does not make a thing to be simply, but only to be hot. Therefore by the coming of the accidental form a thing is not said to be made or generated simply, but to be made such, or to be in some particular condition; and in like manner, when an accidental form is removed, a thing is said to be corrupted, not simply, but relatively. Now the substantial form gives being simply; therefore by its coming a thing is said to be generated simply; and by its removal to be corrupted simply. For this reason, the old natural philosophers, who held that primary matter was some actual being--for instance, fire or air, or something of that sort--maintained that nothing is generated simply, or corrupted simply; and stated that "every becoming is nothing but an alteration," as we read, _Phys._ i, 4. Therefore, if besides the intellectual soul there pre-existed in matter another substantial form by which the subject of the soul were made an actual being, it would follow that the soul does not give being simply; and consequently that it is not the substantial form: and so at the advent of the soul there would not be simple generation; nor at its removal simple corruption, all of which is clearly false.
Whence we must conclude, that there is no other substantial form in man besides the intellectual soul; and that the soul, as it virtually contains the sensitive and nutritive souls, so does it virtually contain all inferior forms, and itself alone does whatever the imperfect forms do in other things. The same is to be said of the sensitive soul in brute animals, and of the nutritive soul in plants, and universally of all more perfect forms with regard to the imperfect.
Reply Obj. 1: Aristotle does not say that the soul is the act of a body only, but "the act of a physical organic body which has life potentially"; and that this potentiality "does not reject the soul."
Whence it is clear that when the soul is called the act, the soul itself is included; as when we say that heat is the act of what is hot, and light of what is lucid; not as though lucid and light were two separate things, but because a thing is made lucid by the light.
In like manner, the soul is said to be the "act of a body," etc., because by the soul it is a body, and is organic, and has life potentially. Yet the first act is said to be in potentiality to the second act, which is operation; for such a potentiality "does not reject"--that is, does not exclude--the soul.
Reply Obj. 2: The soul does not move the body by its essence, as the form of the body, but by the motive power, the act of which presupposes the body to be already actualized by the soul: so that the soul by its motive power is the part which moves; and the animate body is the part moved.
Reply Obj. 3: We observe in matter various degrees of perfection, as existence, living, sensing, and understanding. Now what is added is always more perfect. Therefore that form which gives matter only the first degree of perfection is the most imperfect; while that form which gives the first, second, and third degree, and so on, is the most perfect: and yet it inheres to matter immediately.
Reply Obj. 4: Avicenna held that the substantial forms of the elements remain entire in the mixed body; and that the mixture is made by the contrary qualities of the elements being reduced to an average. But this is impossible, because the various forms of the elements must necessarily be in various parts of matter; for the distinction of which we must suppose dimensions, without which matter cannot be divisible. Now matter subject to dimension is not to be found except in a body. But various bodies cannot be in the same place. Whence it follows that elements in the mixed body would be distinct as to situation. And then there would not be a real mixture which is in respect of the whole; but only a mixture apparent to sense, by the juxtaposition of particles.
Averroes maintained that the forms of elements, by reason of their imperfection, are a medium between accidental and substantial forms, and so can be "more" or "less"; and therefore in the mixture they are modified and reduced to an average, so that one form emerges from them. But this is even still more impossible. For the substantial being of each thing consists in something indivisible, and every addition and subtraction varies the species, as in numbers, as stated in _Metaph._ viii (Did. vii, 3); and consequently it is impossible for any substantial form to receive "more" or "less." Nor is it less impossible for anything to be a medium between substance and accident.
Therefore we must say, in accordance with the Philosopher (De Gener.
i, 10), that the forms of the elements remain in the mixed body, not actually but virtually. For the proper qualities of the elements remain, though modified; and in them is the power of the elementary forms. This quality of the mixture is the proper disposition for the substantial form of the mixed body; for instance, the form of a stone, or of any sort of soul.
Whether the Intellectual Soul Is Properly United to Such a Body?
Objection 1: It would seem that the intellectual soul is improperly united to such a body. For matter must be proportionate to the form.
But the intellectual soul is incorruptible. Therefore it is not properly united to a corruptible body.
Obj. 2: Further, the intellectual soul is a perfectly immaterial form; a proof whereof is its operation in which corporeal matter does not share. But the more subtle is the body, the less has it of matter.
Therefore the soul should be united to a most subtle body, to fire, for instance, and not to a mixed body, still less to a terrestrial body.
Obj. 3: Further, since the form is the principle of the species, one form cannot produce a variety of species. But the intellectual soul is one form. Therefore, it should not be united to a body which is composed of parts belonging to various species.
Obj. 4: Further, what is susceptible of a more perfect form should itself be more perfect. But the intellectual soul is the most perfect of souls. Therefore since the bodies of other animals are naturally provided with a covering, for instance, with hair instead of clothes, and hoofs instead of shoes; and are, moreover, naturally provided with arms, as claws, teeth, and horns; it seems that the intellectual soul should not have been united to a body which is imperfect as being deprived of the above means of protection.
_On the contrary,_ The Philosopher says (De Anima ii, 1), that "the soul is the act of a physical organic body having life potentially."
_I answer that,_ Since the form is not for the matter, but rather the matter for the form, we must gather from the form the reason why the matter is such as it is; and not conversely. Now the intellectual soul, as we have seen above (Q. 55, A. 2) in the order of nature, holds the lowest place among intellectual substances; inasmuch as it is not naturally gifted with the knowledge of truth, as the angels are; but has to gather knowledge from individual things by way of the senses, as Dionysius says (Div. Nom. vii). But nature never fails in necessary things: therefore the intellectual soul had to be endowed not only with the power of understanding, but also with the power of feeling. Now the action of the senses is not performed without a corporeal instrument. Therefore it behooved the intellectual soul to be united to a body fitted to be a convenient organ of sense.
Now all the other senses are based on the sense of touch. But the organ of touch requires to be a medium between contraries, such as hot and cold, wet and dry, and the like, of which the sense of touch has the perception; thus it is in potentiality with regard to contraries, and is able to perceive them. Therefore the more the organ of touch is reduced to an equable complexion, the more sensitive will be the