A problem for Thomistic psychology

Aquinas and his followers hold that the rational (human) soul is both (1) the substantial form of the body and (2) separable from the body. But, these two theses, a lot of thinkers have noted (rightly I think), seem incompatible. The Thomists, however, don’t see the dyad as inconsistent; indeed, they even try and show that (1)-(2) are positively compatible.

Why do they fail to see it? In what follows, I’ll try to explain why from an Avicennian perspective.

The reason, it seems to me, is because they fail to grasp what a substance really is i.e., they do not have the correct account of ‘substance’. Let us look at something one of Aquinas’s contemporary followers says about the issue (Feser 2018, 88-101) in order to see an example of the failure I mentioned.

To remove the mystery from Aquinas holding (1)-(2), the author tells us (ibid., 88-89) that we need to understand two things. First, what (on Thomism) is it for the human being to be a substance; and two, the kind of substance the human being is (on Thomism). Now, understanding the first thing involves clarifying what a substance in general is. So, that’s what the author does first (in ibid., 89-91).

The main claim the author makes in that regard, as far as our purposes are concerned, is the following. He says (after giving an example of a substance i.e., a stone, and attributes i.e., solidity, grayness, etc.):

Substances, in general, just are the sorts of things which exist in themselves rather than inhering in anything else, and which are the subjects of those attributes which do of their nature inhere in something else. (ibid., 89)

In the above passage, ‘substance’ is characterized by two features: (i) as being ‘something that exists in itself rather than inhering in something else’ and (ii) as being ‘the subject of attributes’.

Their mistake, it seems to me, occurs precisely at this point. To see the inadequacy of the account, consider the following:

A body, the author agrees, is a composite of (substantial) form and prime matter. Now, consider the s. form itself. What sort of relation does it have to the prime matter? Specifically, does it inhere in the prime matter? If so, then s. form, by their criteria, is not a substance but rather an attribute i.e., of prime matter, where the prime matter serves as the ‘subject’ of said attribute. In this respect, (ii) would be true of prime matter. The question then is: is (i) true of it as well i.e., does it inhere in something else? If no, then, by their criteria, prime matter (contrary to what they hold) would be a substance, and the s. form inhering in it an accident.

The above in mind, turn your attention to the human soul. They hold that it is a substantial form. But, we just saw that substantial forms turned out to be attributes or accidents i.e., inhering in prime matter. If so, then no human soul is separable. In other words, (2) above is false; for, self-evidently, no attribute can exist apart from what it inheres in. Thus, the inconsistency between (1) and (2) becomes evident.

Alternatively, suppose they say s. form does not inhere in prime matter. Well, does it then exist in itself? If so, then given that s. form itself has attributes (e.g., the stone’s s. form has the attribute of being a ‘principle’), it follows that the s. form itself is a substance; for it satisfies (1)-(2). But this conclusion is inconsistent with their views; they don’t think s. forms are substances. And further, it would follow upon them that all substantial forms are separable, if the human soul is separable because of being (1)-(2). So, there’d be nothing special about human souls in that respect. But this too is inconsistent with their doctrine.

They might respond to this last point, saying: ‘the human soul is separable not because it satisfies (1)-(2) but because it has an action apart from matter. And action follows being’. In response, we’d say the following: true, but then it wouldn’t inhere in matter either. For if an activity of the human soul is independent of matter while it is conjoined to matter (the body), and action follows being, then its being is also independent of matter while it is conjoined to matter. And part of what it means for its being to be independent of matter in this context is that it does not inhere in matter i.e., in the way s. form does (and so whose being is not independent of matter). If this is so, then the human soul just wouldn’t be a s. form proper. Thus, it shouldn’t be called one either. Otherwise, one would be committed holding that the human soul inheres in prime matter (as all s. forms do) while the human is ensouled and then, magically, (post-mortem) stops that and starts existing in itself or independently of matter. In sum, again, (1)-(2) are incompatible.

Hence, if you take the Thomistic line, either (1)-(2) are incompatible or the human soul is not special in being separable.

The truth, and the way out of this mess, is to reject, with the Avicennian account, (1). For, briefly put, on the alternative Avicennian account, substance is:

(1*) something that, when it exists, does not exist or inhere in something else as in a subject

where

            x is a subject = x is an entity of a determinate kind or species

On the Avicennian view (1*) applies to s. form. Thus, s. form would be a substance, not an attribute. And this is so even though it is also true on that view that s. form inheres in something else i.e., prime matter. The reason is because s. form doesn’t inhere in it as in a subject; for prime matter is not a ‘subject’ (as defined above). However, s. form would not be separable. For it inheres or exists in something else; and, as said, self-evidently, nothing that inheres in another can exist apart from it.

As for the human soul in particular, on the Avicennian account it would not only be a substance but also separable. The former, because it satisfies (1*); the latter, because (on independent grounds) it does not inhere in anything at all. In the latter respect, the human soul would be radically unlike s. forms as such.  This is why, for the Avicennian, the human soul, as separable, is not and cannot be a s. form strictly speaking. So, it is not called that either, unless in some other, non-technical sense.

Perhaps you’ll say, with another Thomist (Klima 2009, 162-182), something like: ‘the human soul has two ‘modes of being’. By one mode, it is a form; by another, something subsistent. And by latter mode, it is separable.’

That account too, I think, fails. Here’s why (briefly): For the soul to exist, they hold, is nothing but for a (human) body to be alive. Just as for a white color to exist is nothing but for a body to be white. This is what it is for a form (whether substantial or accidental) to be an ‘inherent being’ (as Klima says). But from this, it straightforwardly follows that anything that is an inherent being, cannot exist apart from that in which it inheres. In other words, its existence depends on the latter. On the other hand, for a subsistent being, this is not true. That is, for it to be is not for something else to be or be in some way. Rather, it itself “primarily exists, in the sense that it may exist even if its existence does not actualize anything else” (p. 6). Thus, its existence does not, like in the case of an inherent being, depend on something else (i.e., what it actualizes).

Now here’s the issue: to attribute, as the author does, both modes of being to the human soul i.e., as quo est (inherent being) and quod est (subsistent being) entails a contradiction: the soul can and cannot exist apart from what it actualizes. That is, inherent being entails ontological dependence, subsistent being entails ontological independence. This, I think, is what Klima fails to see i.e., that ‘being quo est’ and ‘being quod est’ have incompatible implicates, such that a single thing cannot have both attributes without contradiction. In sum, if F and G are true of x, but F entails A and G entails B, where A and B are contradictories, then to say x is F and x is G is a contradiction.