Part 1 n.51: "what is meant by 'substance' - a term which does not apply univocally to God and his creatures
In the case of those items which we regard as things or modes of things, it is worthwhile examining each of them separately. By substance we can understand nothing other than a thing which exists in such a way as to depend on no other thing for its existence. And there is only one substance which can be understood to depend on no other thing whatsoever, namely God. In the case of all other substances, we perceive that they can exist only with the help of God's concurrence. Hence the term substance does not apply univocally, as they say in the Schools, to
God and to other things; that is, there is no distinctly intelligibile meaning of the term which is common to God and his creatures.
Note that he doesn't quite ask the question the way an actual scholastic would (Ariew says that during the time Descartes wrote his major works it had been over 20 years since he had ready any scholastic material, and that prior to writing this treatise he requested a few manuels from his friends, manuels which turned out to be Scotistic as the dominant school at Paris at the time was that of the Scotistae). A scholastic, at least during the 13th and 14th centures would ask if being was univocal to God and creatures, substance and accident. Clearly, in this passage Descartes denies that the term substance is univocal to God and creatures. Pickstock has claimed that Descartes and Kant were basically regular old scholastics in virtue of (evil) Scotistic influence, etc., which seems absurd as his whole project is to supplant scholasticism; but perhaps in supplanting it he was also highly conditioned by it. In any case, this is not all that relevant here. One wonders what Scotus would make of this. He clearly thinks the human mind can form concepts that are univocal to God and creatures, and distinguishes four grades. But they are all transcendentals, that is they transcend the categories. The answer would then hinge on whether one thought that being a substance was a pure perfection. I've never seen Scotus say that it was, but I suppose being a substance is better than not being a substance so there may well be a transcendental sense of the term substance, though again, I am not entirely sure Scotus would agree on that. I also doubt that the scholastics would make such a use of dependence and substance; I've read plenty of discussions about substance being being per se yet even Scotus doesn't hasten to add that only God is substance in the true sense (which sounds more like a Thomistic position, in the manner of predication per prius et posterius which Scotus singles out for attack in one of his main arguments for univocity).
Here is the other passage, which may betray more Scotistic influence than the above:
n.52: "The term substance applies univocally to mind and body. How a substance itself is known
But as for corporeal substance and mind (or created thinking substance), these can be understood to fall under this common concept: things that need only the concurrence of God in order to exist. However, we cannot initially become aware of a substance merely through its being an existing thing, since this alone does not of itself have any effect on us. We can, however, easily come to know a substance by one of its attributes, in virtue of the common notion that nothingness possesses no attributes, that is to say, no properties or qualities. Thus, if we perceive the presence of some attribute, we can infer that there must also be present an existing thing or substance to which it may be attributed."
I'm not sure how useful this actually is; his argument that substance is univocal to mind and body is based on a common concept; is this common concept that of substance? It seems rather in his own words to be the fact that they both need divine concurrence in order to exist. But this would make everything univocally a substance, even accidents. I don't know what this is supposed to mean. In any case, we seem to be closer to Scotistic territory here, as Scotus does make the controversial claim that we do not know substance qua substance. Rather, we have a common notion of being common to substance and accidents that allows us to infer substances underlying the accidents that impinge on the senses.
Stay tuned for more "Posts of Interest!"