Yesterday I quoted Peter Geach in exposition of Aquinas' theory of intentionality. I will now quote Anthony Kenny in exposition of the same doctrine:
The form is individuated when existing with esse naturale in an actual example of a species; it is also individuated, in quite a different way, when it exists with esse intentionale in the mind of a thinker. Suppose that I think of a crocodile. There seem to be two things that make this thought the thought that it is: first, that it is a thought of a crocodile and not, say, of an elephant; second, that it is my thought and not yours or President Bush's. Other things may be true of thoughts -- e.g. that they are interesting, obsessive, vague -- but these seem to be the two things essential to any thoughts: that they should be someone's thoughts, and that they should be thoughts of something. The theory of intentionality is meant to set out both these features. The form of crocodile when existing in nature is individuated by the matter it informs; when existing intentionally, it is individuated by the person in whose mind it exists. (Aquinas on Being, Oxford 2002, p. 169)
The idea, then, is that one and the same form is both in the thing outside the mind (the crocodile in Kenny's example) and in the mind of the person who is thinking about the crocodile. It is this self-same form that makes the thought a thought of a crocodile as opposed to a thought of something else. But the form exists in mind and in thing in two different ways. It exists in the mind with esse intentionale (intentional be-ing), but exists in the thing with esse naturale (natural be-ing). (My use of 'be-ing' to translate esse is not for the sake of being cute but to underscore the crucial distinction between the infinitive esse (to be) and the present participle ens, both of which can be translated with 'being.')
The distinction between the two modes of be-ing is needed in order to avoid the consequence that a mind thinking about a crocodile either has a crocodile in it or is itself a crocodile. A thought of a red sunset is not a red thought, and a thought of a crocodile does not have the properties characteristic of a crocodile.
I now pass over to critique. Let's first note a distinction that I fudged yesterday for the sake of brevity, brevity being the soul of blog. Reverting to yesterday's example, it is the distinction between thinking of a cat (some cat or other) and thinking of a particular cat such as Max Black. It is one thing to explain how my thought of a cat is a thought of a cat (as opposed to a dog or a kangaroo), and quite another to explain how my thought of Max the cat is a thought of Max. The Thomist theory may well be up to the first task. But I'm not sure it is up to the second.
Matter is the principium individuationis. What makes a cat an individual cat numerically distinct from other cats is its signate or designated matter (materia signata). In extramental reality, then, Max's individuality is bound up with his signate matter. But when Max's form exists in my mind with esse intentionale, it is exists in an immaterial way. What then individuates Max's form as it exists in my mind with esse intentionale? And if nothing individuates it, then what makes my thought of Max the cat a thought of Max (as opposed to a thought of some cat or other)?
I hope to expatiate further on this tomorrow.