This is proving to be a fascinating topic. Let's push on a bit further.
Aquinas says that any given nature can be considered in three ways: in respect of the esse it has in concrete singulars; in respect of the esse it has in minds; absolutely, in the abstract, without reference to either mode of esse. The two modes are esse naturale (esse reale) and esse intentionale. We can speak of these in English as real existence and intentional existence.
According to Schopenhauer, the medievals employed but three examples: Socrates, Plato, and an ass. Who am I to deviate from a tradition at once so hoary and noble? So take Socrates. Socrates is human. The nature humanity exists really in him, and in Plato, but not in the ass. The same nature exists intentionally in a mind that thinks about or knows Socrates. For Aquinas, there are no epistemic deputies standing between mind and thing: thought reaches right up to and grasps the thing itself. There is an isomorphism between knowing mind and thing known. The ground of this isomorphism is the natura absoluta, the nature considered absolutely. Call it the common nature (CN). It is so-called because it is common to both the knower and the known, informing both, albeit in different ways. It is also common to all the singulars of the same nature and all the thoughts directed to the same sort of thing. So caninity is common to all doggy thoughts, to all dogs, besides linking the doggy thoughts to the dogs.
My concern over the last few days has been the exact ontological status of the CN.
This morning, with the help of Anthony Kenny, I realized that there are four possible views, not three as I stated earlier:
A. The CN really exists as a separate, self-subsistent item.
B. The CN exists only intentionally in the mind of one who abstracts it from concrete singulars and mental acts.
C. The CN has Meinongian Aussersein status: it has no mode of being whatsoever, and yet is is something, not nothing. It actually has properties, but is property-incomplete (and therefore in violation of LEM) in that it is neither one nor many, neither universal nor particular, neither intentionally existent nor really existent.
D. The CN exists intentionally in the mind of God, the creator.
(A) is a nonstarter and is rejected by both me and Lukas Novak. (B) appears to be Novak's view. (C) is the interpretation I was tentatively suggesting. My thesis was that the CN must have Aussersein status, but then it inherits -- to put it anachronistically -- all the problems of Meinongianism. The doctor angelicus ends up with Meinongian monkey on his back.
Let me now try to explain why I reject (B), Novak's view, and incline toward (C), given that (A) cannot possibly be what Aquinas had in mind.
Consider a time t before there were any human animals and any finite minds, and ask yourself: did the nature humanity exist at t? The answer has to be in the negative if there are only two modes of existence, real existence in concrete singulars and intentional existence in finite (creaturely) minds. For at t there were no humans and no finite minds. But surely it is true at t that man is rational, that humanity includes rationality. This implies that humanity at t cannot be just nothing at all. For if it were nothing at all at t, then 'Man is rational'' at t would lack a truth-maker. Furthermore, we surely don't want to say that 'Man is rational' first becomes true when the first human being exists. In some sense, the common nature must be prior to its existential realization in concrete singulars and in minds. The common nature cannot depend on these modes of realization. Kenny quotes Aquinas (Aquinas on Being, Oxford 2002, p. 73):
Socrates is rational, because man is rational, and not vice versa; so that even if Socrates and Plato did not exist, rationality would still be a characteristic of human nature.
Socrates est rationalis, quia home est rationalis, et no e converso; unde dato quod Socrates et Plato non essent, adhuc humanae naturae rationalitas competeret. (Quodl. VIII, I, c, 108-110)
Aquinas' point could be put like this. (i) At times and in possible worlds in which humans do not exist, it is nevertheless the case that rationality is included in humanity, and (ii) the metaphysical ground of humans' being rational is the circumstance that rationality is included in humanity, and not vice versa.
Now this obviously implies that the CN humanity has some sort of status independent of real and intentional existence. So we either go the Meioningian route or we say that CNs exist in the mind of God. Kenny:
Aquinas' solution is to invoke the divine mind. There are really four, not three ways of considering natures: first, as they are in the mind of the creator; second, as they are in the abstract; theitrs, as they are in individuals; and finally, as they are in the human mind. (p. 74)
This may seem to solve the problem I raised. CNs are not nothing because they are divine accusatives. And they are not nothing in virtue of being ausserseiend. This solution avoids the three options of Platonism, subjectivism (according to which CNs exist only as products of abstraction), and Meinongianism.
The problem with the solution is that it smacks of deus ex machina: God is brought in to solve the problem similarly as Descartes had recourse to the divine veracity to solve the problem of the external world. One ought to be forgiven for thinking that solutions to the problems of universals, predication, and intentionality ought to be possible without bringing God into the picture. But this is a separate can of worms.