Summa contra Gentiles2.59 Chapter LIX. THAT man's possible INTELLECT IS NOT A SEPARATE SUBSTANCE

Others there have been, who discovered another reason for maintaining that the intellectual soul cannot be united to the body as its form. For they say that the intellect which Aristotle calls possible, is a separate substance not united to us as a form.

They endeavour to prove this from the words of Aristotle, who says, speaking of this intellect, that it is separate, not mixed with the body, simple, impassible; which could not be said of it, if it were the body’s form.

Also, from the demonstration whereby he proves that, since the possible intellect receives all the species of sensible things through being in potentiality to them, it must needs lack them all. Even so the pupil which receives the species of all colours, lacks all colour; for if by itself it had any colour, that colour would prevent it seeing other colours; in fact it would see nothing but under that colour. The same would happen with the possible intellect, if by itself it had any form or nature of sensible things. Yet it would have to be so if it were bound up with the body. Likewise, if it were the form of a body: because, since from form and matter there is made one thing, the form must participate something of the nature of which it is the form. Consequently it is impossible that the possible intellect be bound up with the body, or be the act or form of a body.

Further. If it were the form of a material body, the receptivity of such an intellect would be of the same kind as the receptivity of primary matter; because that which is the form of a body, receives nothing without its matter. Now primary matter receives individual forms, in fact they are individualized through being in matter. Therefore the possible intellect would receive forms as they are individual: and consequently would not be cognizant of universals, which is clearly false.

Further. Primary matter is not cognizant of the forms which it receives. Consequently if the receptivity of the possible intellect were the same as of primary matter, neither would the possible intellect know the forms it receives: and this is false.

Moreover. There cannot possibly be an infinite power in a body, as proved by Aristotle (8 Phys.). Now the possible intellect is, in a manner, of infinite power, since by it we judge of an infinite number of things, inasmuch as by it we know universals, under which potentially infinite particulars are contained. Therefore the possible intellect is not a power in a body.

For these reasons Averroes was moved, and likewise some of the ancients, as he says, to hold that the possible intellect, by which the soul understands, has a separate being from the body, and is not the form of the body.

Since however such an intellect would nowise belong to us, nor should we understand thereby, unless it were in some way united to us, he defines the way in which it comes into touch with us, saying that the species actually understood is the form of the possible intellect, just as the actually visible is the form of the visual power. Hence there results one thing from the possible intellect and the actually understood form. Consequently the possible intellect is united to whomsoever the aforesaid understood form is united. Now it is united to us by means of the phantasm which is a kind of subject of that understood form: and in this way the possible intellect also is in touch with us.

But it is easy to see that all this is nonsensical and impossible. For the one who understands is the one who has intellect. And the thing understood is the thing whose intelligible species is united to the intellect. Consequently though the intelligible species united to the intellect is in a man in some way, it does not follow that the man is the one who understands, but only that he is understood by the separate intellect.

Further. The actually understood species is the form of the possible intellect, as the visible species in act is the form of the visual power, or of the eye itself. Now the understood species is compared to the phantasm as the visible species in act is compared to the coloured object outside the soul: in fact he uses this comparison himself, as also does Aristotle. Therefore by the intelligible form the possible intellect is in touch with the phantasm which is in us, in the same way as the visual power with the colour that is in the stone. But this contact does not make the stone to see but to be seen. Therefore also the aforesaid contact of the possible intellect with us, does not make us to understand, but only to be understood. Now it is clear that it is properly and truly said that man understands, for we would not inquire into the nature of the intellect except for the fact that we understand ourselves. Therefore the aforesaid manner of contact is not sufficient.

Again. Every knower by its cognitive power is united to its object, and not vice versa, just as every operator by its operative power is united to the thing operated. Now man is intelligent by his intellect as by his cognitive power. Therefore he is not united to the intellect by the intelligible form, but by the intellect he is united to the intelligible.

Moreover. That by which a thing operates must be its form, for nothing acts except in so far as it is in act, and a thing is not in act except by that which is its form; wherefore Aristotle proves that the soul is a form, from the fact that an animal lives and senses through the soul. Now man understands, and this by his intellect only: wherefore Aristotle when inquiring into the principle whereby we understand describes to us the nature of the possible intellect. Therefore the possible intellect must be united to us formally and not merely by its object.

Further. The intellect in act and the intelligible in act are one, just as the sense in act and the sensible in act. Not so however are the intellect in potentiality and the intelligible in potentiality, nor the sense in potentiality and the sensible in potentiality. Wherefore the species of a thing according as it is in the phantasms is not actually intelligible, for it is not thus that it is one with the intellect in act, but as abstracted from the phantasms: even so neither is the species of colour actually perceived according as it is in the stone, but only according as it is in the pupil. Now according to the opinion stated above the intelligible species is in contact with us only according as it is in the phantasms. Therefore it is not in contact with us according as it is one with the possible intellect as its form. Consequently it cannot be the means of bringing the possible intellect into contact with us: since according as it is in contact with the possible intellect it is not in contact with us, nor vice versa.

Now it is evident that he who devised this opinion was deceived by an equivocation. For colours existing outside the soul, given the presence of light, are actually visible as being able to move the sight, and not as actually perceived, according as they are one with the sense in act. In like manner the phantasms are made actually intelligible by the light of the active intellect, so that they can move the possible intellect, but not so that they be actually understood, according as they are one with the possible intellect made actual.

Again. Where the living thing has a higher operation, there is a higher kind of life corresponding to that operation. For in plants we find only an action pertaining to nutrition. In animals we find a higher operation, namely sensation and local movement: wherefore the animal lives by a higher kind of life. But in man we find a yet higher vital operation than in the animal, namely intelligence. Therefore man must have a higher kind of life. Now life is through the soul. Therefore man will have a higher soul, whereby he lives, than is the sensitive soul. But none is higher than the intellect. Therefore the intellect is man’s soul: and consequently it is his form.

Further. That which is consequent on the operation of a thing, does not give a thing its species: because operation is a second act, whereas the form whereby a thing has species is the first act. Now the union of the possible intellect with man, according to the above opinion, is consequent on man’s operation: for it takes place through the medium of the phantasm which, according to the Philosopher, is a movement resulting from the sense in act. Therefore man does not take his species from that union: and consequently man differs from dumb animals by the fact that he has an intellect.

Moreover. If man takes his species from being rational and having an intellect, whoever is in the human species, is rational and intelligent. But a child, even before leaving the womb, is in the human species: and yet it has not phantasms that are actually intelligible. Therefore a man has not an intellect through the intellect being in contact with man by means of an intelligible species the subject of which is a phantasm.