Summa Th. I EN Qu.76 a.3
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 (Question [75], Article [6]). Therefore in man the essence of the intellectual soul, the sensitive soul, and the nutritive soul, cannot be the same.
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.
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 to Objection: 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.
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.
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 shown further on (Question [118], Article [2], ad 2).
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.
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.
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.
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.
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 (Article [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 to Objection: 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.
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.
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.
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.
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.
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.
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.
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 (Question [55], Article [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 touch. But the intellectual soul has the power of sense in all its completeness; because what belongs to the inferior nature pre-exists more perfectly in the superior, as Dionysius says (Div. Nom. v). Therefore the body to which the intellectual soul is united should be a mixed body, above others reduced to the most equable complexion. For this reason among animals, man has the best sense of touch. And among men, those who have the best sense of touch have the best intelligence. A sign of which is that we observe "those who are refined in body are well endowed in mind," as stated in De Anima ii, 9.
Reply to Objection: 1. Perhaps someone might attempt to answer this by saying that before sin the human body was incorruptible. This answer does not seem sufficient; because before sin the human body was immortal not by nature, but by a gift of Divine grace; otherwise its immortality would not be forfeited through sin, as neither was the immortality of the devil.
Therefore we answer otherwise by observing that in matter two conditions are to be found; one which is chosen in order that the matter be suitable to the form; the other which follows by force of the first disposition. The artisan, for instance, for the form of the saw chooses iron adapted for cutting through hard material; but that the teeth of the saw may become blunt and rusted, follows by force of the matter itself. So the intellectual soul requires a body of equable complexion, which, however, is corruptible by force of its matter. If, however, it be said that God could avoid this, we answer that in the formation of natural things we do not consider what God might do; but what is suitable to the nature of things, as Augustine says (Gn ad lit. ii, 1). God, however, provided in this case by applying a remedy against death in the gift of grace.
2. A body is not necessary to the intellectual soul by reason of its intellectual operation considered as such; but on account of the sensitive power, which requires an organ of equable temperament. Therefore the intellectual soul had to be united to such a body, and not to a simple element, or to a mixed body, in which fire was in excess; because otherwise there could not be an equability of temperament. And this body of an equable temperament has a dignity of its own by reason of its being remote from contraries, thereby resembling in a way a heavenly body.
3. The parts of an animal, for instance, the eye, hand, flesh, and bones, and so forth, do not make the species; but the whole does, and therefore, properly speaking, we cannot say that these are of different species, but that they are of various dispositions. This is suitable to the intellectual soul, which, although it be one in its essence, yet on account of its perfection, is manifold in power: and therefore, for its various operations it requires various dispositions in the parts of the body to which it is united. For this reason we observe that there is a greater variety of parts in perfect than in imperfect animals; and in these a greater variety than in plants.
4. The intellectual soul as comprehending universals, has a power extending to the infinite; therefore it cannot be limited by nature to certain fixed natural notions, or even to certain fixed means whether of defence or of clothing, as is the case with other animals, the souls of which are endowed with knowledge and power in regard to fixed particular things. Instead of all these, man has by nature his reason and his hands, which are "the organs of organs" (De Anima iii), since by their means man can make for himself instruments of an infinite variety, and for any number of purposes.
Objection: 1. It would seem that the intellectual soul is united to the body through the medium of accidental dispositions. For every form exists in its proper disposed matter. But dispositions to a form are accidents. Therefore we must presuppose accidents to be in matter before the substantial form; and therefore before the soul, since the soul is a substantial form.
2. Further, various forms of one species require various parts of matter. But various parts of matter are unintelligible without division in measurable quantities. Therefore we must suppose dimensions in matter before the substantial forms, which are many belonging to one species.
3. Further, what is spiritual is connected with what is corporeal by virtual contact. But the virtue of the soul is its power. Therefore it seems that the soul is united to the body by means of a power, which is an accident.
On the contrary Accident is posterior to substance, both in the order of time and in the order of reason, as the Philosopher says, Metaph. vii (Did. vi, 1). Therefore it is unintelligible that any accidental form exist in matter before the soul, which is the substantial form.
I answer that If the soul were united to the body, merely as a motor, there would be nothing to prevent the existence of certain dispositions mediating between the soul and the body; on the contrary, they would be necessary, for on the part of the soul would be required the power to move the body; and on the part of the body, a certain aptitude to be moved by the soul.
If, however, the intellectual soul is united to the body as the substantial form, as we have already said above (Article [1]), it is impossible for any accidental disposition to come between the body and the soul, or between any substantial form whatever and its matter. The reason is because since matter is in potentiality to all manner of acts in a certain order, what is absolutely first among the acts must be understood as being first in matter. Now the first among all acts is existence. Therefore, it is impossible for matter to be apprehended as hot, or as having quantity, before it is actual. But matter has actual existence by the substantial form, which makes it to exist absolutely, as we have said above (Article [4]). Wherefore it is impossible for any accidental dispositions to pre-exist in matter before the substantial form, and consequently before the soul.
Reply to Objection: 1. As appears from what has been already said (Article [4]), the more perfect form virtually contains whatever belongs to the inferior forms; therefore while remaining one and the same, it perfects matter according to the various degrees of perfection. For the same essential form makes man an actual being, a body, a living being, an animal, and a man. Now it is clear that to every "genus" follow its own proper accidents. Therefore as matter is apprehended as perfected in its existence, before it is understood as corporeal, and so on; so those accidents which belong to existence are understood to exist before corporeity; and thus dispositions are understood in matter before the form, not as regards all its effects, but as regards the subsequent effect.
2. Dimensions of quantity are accidents consequent to the corporeity which belongs to the whole matter. Wherefore matter, once understood as corporeal and measurable, can be understood as distinct in its various parts, and as receptive of different forms according to the further degrees of perfection. For although it is essentially the same form which gives matter the various degrees of perfection, as we have said (ad 1), yet it is considered as different when brought under the observation of reason.
3. A spiritual substance which is united to a body as its motor only, is united thereto by power or virtue. But the intellectual soul is united by its very being to the body as a form; and yet it guides and moves the body by its power and virtue.
Objection: 1. It seems that the soul is united to the animal body by means of a body. For Augustine says (Gn ad lit. vii, 19), that "the soul administers the body by light," that is, by fire, "and by air, which is most akin to a spirit." But fire and air are bodies. Therefore the soul is united to the human body by means of a body.
2. Further, a link between two things seems to be that thing the removal of which involves the cessation of their union. But when breathing ceases, the soul is separated from the body. Therefore the breath, which is a subtle body, is the means of union between soul and body.
3. Further, things which are very distant from one another, are not united except by something between them. But the intellectual soul is very distant from the body, both because it is incorporeal, and because it is incorruptible. Therefore it seems to be united to the body by means of an incorruptible body, and such would be some heavenly light, which would harmonize the elements, and unite them together.
On the contrary The Philosopher says (De Anima ii, 1): "We need not ask if the soul and body are one, as neither do we ask if wax and its shape are one." But the shape is united to the wax without a body intervening. Therefore also the soul is thus united to the body.
I answer that If the soul, according to the Platonists, were united to the body merely as a motor, it would be right to say that some other bodies must intervene between the soul and body of man, or any animal whatever; for a motor naturally moves what is distant from it by means of something nearer.
If, however, the soul is united to the body as its form, as we have said (Article [1]), it is impossible for it to be united by means of another body. The reason of this is that a thing is one, according as it is a being. Now the form, through itself, makes a thing to be actual since it is itself essentially an act; nor does it give existence by means of something else. Wherefore the unity of a thing composed of matter and form, is by virtue of the form itself, which by reason of its very nature is united to matter as its act. Nor is there any other cause of union except the agent, which causes matter to be in act, as the Philosopher says, Metaph. viii (Did. vii, 6).
From this it is clear how false are the opinions of those who maintained the existence of some mediate bodies between the soul and body of man. Of these certain Platonists said that the intellectual soul has an incorruptible body naturally united to it, from which it is never separated, and by means of which it is united to the corruptible body of man. Others said that the soul is united to the body by means of a corporeal spirit. Others said it is united to the body by means of light, which, they say, is a body and of the nature of the fifth essence; so that the vegetative soul would be united to the body by means of the light of the sidereal heaven; the sensible soul, by means of the light of the crystal heaven; and the intellectual soul by means of the light of the empyrean heaven. Now all this is fictious and ridiculous: for light is not a body; and the fifth essence does not enter materially into the composition of a mixed body (since it is unchangeable), but only virtually: and lastly, because the soul is immediately united to the body as the form to matter.
Reply to Objection: 1. Augustine speaks there of the soul as it moves the body; whence he uses the word "administration." It is true that it moves the grosser parts of the body by the more subtle parts. And the first instrument of the motive power is a kind of spirit, as the Philosopher says in De causa motus animalium (De mot. animal. x).
2. The union of soul and body ceases at the cessation of breath, not because this is the means of union, but because of the removal of that disposition by which the body is disposed for such a union. Nevertheless the breath is a means of moving, as the first instrument of motion.
3. The soul is indeed very distant from the body, if we consider the condition of each separately: so that if each had a separate existence, many means of connection would have to intervene. But inasmuch as the soul is the form of the body, it has not an existence apart from the existence of the body, but by its own existence is united to the body immediately. This is the case with every form which, if considered as an act, is very distant from matter, which is a being only in potentiality.
Summa Th. I EN Qu.76 a.3