The 'thin' conception of being or existence entails that there are no modes of being. Most analytic philosophers accept the thin conception and reject modes of being. Flying in the face of analytic orthodoxy, I maintain that the modes-of-being doctrine, the MOB doctrine if you will, is defensible. Indeed, I should like to say something stronger, namely, that it is indispensable for metaphysics, although I won't argue for the stronger claim here.
My task is not to specify what the modes of being are, but the preliminary one of defending the very idea of there being different modes of being. So I plan to look at a range of examples without necessarily endorsing the modes of being they involve.
This post focuses on substances and accidents and argues that an accident and a substance of which it is the accident differ in their very mode of being, and not merely in their respective natures.
D1. S is a (primary) substance =df S is metaphysically capable of independent existence.
D2. A is an accident =df A is not metaphysically capable of independent existence, but exists, if it exists, in a substance.
By 'metaphysically' I mean broadly logically in A. Plantinga's sense. So if a particular statue is a substance, then it is broadly logically possible that it exist even if nothing else exists. And if the smoothness or color of the statue are accidents, then it is broadly logically impossible that they exist (i) apart from some substance or other and indeed (ii) apart from the very substance of which they are the accidents.
The second point implies that accidents are particulars, not universals. Accidents cannot be shared. They are not 'repeatable' in the manner of universals. Nor can they 'migrate' from one substance to another. You can't literally catch my cold if my cold is an accident of me as substance. Your cold is your numerically distinct cold. Socrates' whiteness is his whiteness and is as such numerically distinct from Plato's whiteness. The connection between a substance and its accidents is an intimate one. But it is an intimacy shy of identity. A substance has accidnet; it cannot therefore be identical to any one of them or even the whole lot of them.
2. Now suppose there is a substance S and an accident A of S. I do not deny that there is a sense of 'exist' according to which both S and A exist and exist in the very same way. Suppose that S and A are the only two items that exist. Then of course there is a sense in which both items exist: each is something and not nothing. Both are there to be quantified over. We can say '(∃x)(x = S)' and '(∃x)(x = A)': 'Something is (identically) S' and 'Something is (identically) A.'
3. Now the issue is this: Does what I said in #2 exhaust what there is to be said about the being or existence of S and A? On the thin conception, that is all there is to it. To be is to be something or other. If there are substances and accidents then both are in the same sense and in the same mode. ('Sense' a semantic term; 'mode' an ontological term.) Since S and A both exist in the same way on the thin conception, they are not distinguished by their mode of being. They are distinguished by their respective natures alone.
4. In order to see what is wrong with the thin conception, let us ask how the two entities S and A are related. Indeed, can one speak of a relation at all? Traditionally, one speaks of inherence: A inheres in S. Inherence cannot be an external relation since if a and b are externally related, then a and b can each exist apart from the relation. But A cannot exist apart from the inherence 'relation' to S. On the other hand, if S and A were internally related, then neither could exist without the other. But S can exist without A. Since S can exist without A, but A cannot exist without S, A is existentially dependent on S, dependent on S for its very existence, while S is capable of independent existence. But this is just to say that A exists in a different way than S exists. Thus S and A differ in their mode of being. One cannot make sense of inherence without distinguishing substantial and accidental modes of being.
5. In sum: Talk of substances and their accidents is intelligible. But it is intelligible only if there are two modes of being, substantial and accidental. Therefore, talk of modes of being is intelligible. Since the thin conception of being entails the unintelligibility of modes of being, the thin conception ought to be rejected.