CT 85: Unity of the Possible Intellect (Part III)

I began discussing this chapter of St. Thomas’ Compendium Theologiae back around the end of April; finally, two months later, I’m getting back to it. In order to understand this post you’ll want to revisit Part I and Part II of the discussion.

I’ve just re-read them myself, in preparation to continue, and I think they hold up OK. There’s one point I’d like to clarify. In Part I, I say

And then you’ve got humans, who are individuated by matter, as animals are, but have an intellectual (and hence immaterial) soul, as angels do.

This is not quite right: an angel does not have an intellectual and immaterial soul; rather, an angel is an intellectual and immaterial spirit. The human soul is also intellectual and immaterial spirit.

But this is a nit.

In Part II, Thomas speaks of those who would say that all men share a single Soul. Having described that position, he now goes on to explain how every man can have a unique soul while remaining members of the one species.

The absurdity of this whole position is easily perceived.


To make this clear, let us proceed as one would proceed against those who deny fundamental principles. That is, let us establish a truth that simply cannot be denied. Let us suppose that this man, for example, Socrates or Plato, understands. Our adversary could not deny that the man understands, unless he knew that it ought to be denied. By denying he affirms, for affirmation and denial are intelligent actions.

Thomas is, I gather, trying to prove that man can understand to one who denies it. He posits that Socrates can understand. The denier cannot rationally deny that Socrates understands unless the denier has a good reason. But if denier has a good reason, that reason is an act of understanding! Therefore, the denier must either affirm that Socrates understands or, in denying it, affirm that he himself understands. Thus, it is possible for a man to understand.

(Remember that for Thomas, to understand is to know intellectually. If I see a dog, the appearance of the dog is present to my Sense: I perceive the dog, I have a perception. When I recognize that I perceive a dog, the concept dog is now present to my intellect, and I understand that this object before me is a dog.)

If, then, the man in question understands, that whereby he formally understands must be his form, since nothing acts unless it is in act.

There is act, that which is, and potency, that which could be. I am here; I could be there. I am hungry; I could be full. I am thinking; I could be asleep. Anything that I actually am, or actually do, involves bringing something potential into actuality. That’s the first thing. And the second thing is, actuality always involves form.

When I understand something in actuality, rather than just potentially, I am acting; and that by which I understand, as a formal cause of my understanding, is my form.

Hence that whereby an agent acts, is his act; just as the heat by which a heated body causes warmth, is its act. Therefore the intellect whereby a man understands is the form of this man, and the same is true of another man.

My intellect is my form; and your intellect is your form.

But the same numerical form cannot belong to numerically different individuals, for numerically different individuals do not possess the same existence; and yet everything has existence by reason of its form. Accordingly the intellect whereby a man understands cannot be but one in all men.

What makes me me is mine; and what makes you you is yours. These are two separate, numerically distinct things. What makes me me is my form, and as shown above my form is my intellect. The same applies to you. Thus, my intellect and your intellect are distinct.

Perceiving the force of this difficulty, some endeavor to find a way of escaping it. They say that the possible intellect, of which there was question above, receives the intelligible species by which it is reduced to act. These intelligible species are, in some way, in the phantasms. Hence the possible intellect is continuous and is joined to us so far as the intelligible species is both in the possible intellect and in the phantasms that are in us. It is thus that we are able to understand through the agency of the possible intellect.

Now things get a little difficult. (Now? Now, he says?) We need to review some background.

Every man has Intellect and Sense. Sense is the faculty with which we sense the outside world through our sight, smell, taste, touch, and hearing; it’s also the faculty whereby we imagine things of this sort. When I see my son, there is an image in my Sense. When I picture the face of my son, I am using my imagination: I am bringing forth an image from my memory. Again, the image is in my Sense. This kind of image, however derived, and whichever senses are involved, is what Thomas means by a “phantasm”.

Now, the Sense belongs to our animal nature: every animal has it to a greater or lesser degree. It is, consequently, an aspect of our material bodies, and in particular of our brains.

Our Intellect, as we’ve said before, is immaterial: non-human animals have no intellect, and cannot be said to be rational.

Now, there is a link between the Sense and the Intellect. We see the world, resulting in phantasms in our Sense. Our Intellect apprehends the natures of these phantasms, resulting in intelligible species in our possible intellect.

At this point, you should probably go back and re-read the last quoted passage.

There are those who insist that Intellect is one, that all humans share one Intellect. But our Intellect is our form, that which gives us existence; we must each have our own. Those who insist that the intellect is one try to get around this by pointing out the link between the Intellect and the Sense. The intelligible species understood by the Intellect are somehow present in the phantasms perceived by the Sense. This roots the shared Intellect in the individual man’s Sense, and makes it appear individuated without its really being so.

So they say, but Thomas strongly disagrees:

Unfortunately for this solution, it is utterly valueless.

This is a remarkably strong statement for Thomas; he’s usually more understated.

In the first place, the intelligible species, as it exists in the phantasms, is a concept only in potency; and as it exists in the possible intellect, it is a concept in act. As existing in the possible intellect, it is not in the phantasms, but rather is abstracted from the phantasms. Hence no union of the possible intellect with us remains.

We understand intelligible species, or (as we would say today) concepts. The concepts are present in the phantasms in potency only, not in act; the Intellect brings them into act by abstracting them from the phantasms. If the Intellect is one and shared by all men, then “no union of the possible intellect with us remains.”

Secondly, even granting that there may be some sort of union, this would not suffice to enable us to understand. The presence of the species of some object in the intellect does not entail the consequence that the object understands itself, but only that it is understood; a stone does not understand, even though a species of it may be in the possible intellect. Hence, from the fact that species of phantasms present in us are in the possible intellect, it does not follow that we thereupon understand. It only follows that we ourselves, or rather the phantasms in us, are understood.

If I perceive a stone, a phantasm of that stone appears in my Sense. And if there is a sufficient union of my Sense with this “shared intellect”, as Thomas denies, that the concept Stone appears in the shared intellect, this means that the Stone is understood by the shared intellect; it does not mean that I, an individual, am the one who understands Stone.

This will appear more clearly if we examine the comparison proposed by Aristotle in Book III of De anima [7, 431 a 14], where he says that the intellect is to phantasm what sight is to color. Manifestly, the fact that the species of colors on a wall are in our vision does not cause the wall to see, but to be seen. Likewise, the fact that the species of the phantasms in us come to be in the intellect, does not cause us to understand, but to be understood.

If the intellect that understands my phantasms is not mine, then I am understood, but I cannot say that I understand.

Further, if we understand formally through the intellect, the intellectual action of the intellect must be the intellectual action of the man, just as the heating action of fire and of heat are the same. Therefore, if intellect is numerically the same in me and in you, it follows that, with respect to the same intelligible object, my action of understanding must be the same as yours, provided, of course, both of us understand the same thing at the same time. But this is impossible, for different agents cannot perform one and the same numerical operation. Therefore it is impossible for all men to have but a single intellect.

My understanding is my understanding, and your understanding is yours. We can both understand the same thing, but not by the same act.

Consequently, if the intellect is incorruptible, as has been demonstrated many intellects, corresponding to the number of men, will survive the destruction of their bodies.

Thus, every man must have his own Intellect. And since the Intellect is incorruptible, then when men die their Intellects remain.

I think I understood some of that, but certainly not all of it.

In the next part, we’ll look at Thomas’ answer to the objections listed in Part II.

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