Some, Thomas tells us, would conclude from the immaterial nature of the possible intellect that all men must share a single intellect, and hence a single soul. As he says,
An objector may say: the intellect is indeed incorruptible, but there is only one intellect in all men; and so what remains after the corruption of all men is but one. That there is only one intellect for all men, the objector may continue, can be established on many grounds.
So much we said yesterday.
First, on the part of the intelligible species. If I have one intellect and you have another, there will have to be one intelligible species in me and another in you, and consequently there will be one object that I understand and another that you understand. Hence the intelligible species will be multiplied according to the number of individuals, and so it will not be universal but individual. The conclusion would then seem to follow that it is understood not in act, but only in potency; for individual species are intelligible in potency, not in act.
When I apprehend an object, what I have in my possible intellect is its intelligible species. And indeed, this intelligible species will be multiplied by the number of individuals. So how can the intelligible species be a universal? (The answer, as we will see, is that it isn’t, and that’s OK.) The meaning of the italicized sentence eludes me tonight.
Moreover, since the intellect, as we have seen, is a substance subsisting in its own being, and since intellectual substances that are numerically many do not belong to one species, as we have also seen, it follows that if I have one intellect and you have another that is numerically different, the two must differ specifically. And so you and I would not belong to the same species.
I talked about this yesterday. To be numerically many, the object says, two beings must either be of different species, as angels are, or of the same species and distinguished by having different matter, as animals are. Thomas is going to choose a third option.
Furthermore, since all individuals share in one specific nature, there must be something besides specific nature whereby individuals may be distinguished from one another. Accordingly, if there is one specific intellect in all men, but many intellects that are numerically distinct, something must be found that will make one intellect differ numerically from another. This cannot be anything pertaining to the substance of the intellect, since the intellect is not composed of matter and form. Consequently any difference that might be admitted, on the part of the substance of the intellect, would be a formal difference that would cause diversity in the species. The only possibility left is that the intellect of one man cannot differ numerically from the intellect of another man except by reason of the diversity of their bodies. Therefore, when the various bodies corrupt, it seems that only one intellect, and not a plurality of intellects, would remain.
Something distinguishes one man from another, and it appears to be the possession of a body. For my intellect to be distinct from yours, while being immaterial, would seem to make us be of two different species, which is not the case. Thus, when I die and you die, there’s nothing to distinguish the intellect that remains. I take it that this is another way of saying the previous point.
The absurdity of this whole position is easily perceived….
But that’s another post.