Bill Vallicella gives a very thorough and illuminating account of the “thin theory” of existence. He shows how it is fundamental to the divide between Analytic and Continental philosophy, gives an account of where the idea comes from and shows exactly what it consists in. Vallicella explains the essence of the theory starting with a quotation from Van Inwagen:
“The thin conception of being is this: the concept of being is closely allied with the concept of number: to say that there are Xs is to say that the number of Xs is 1 or more — and to say nothing more profound, nothing more interesting, nothing more.” (p. 4) Connoisseurs of this arcana will recognize it as pure Frege:
. . . existence is analogous to number. Affirmation of existence is
in fact nothing but denial of the number nought. (Gottlob Frege,
Foundations of Arithmetic, 65e)
‘Cats exist,’ then, says that the number of cats is one or more. Equivalently, it says that the concept cat has one or more instances. Existence, as Frege puts it, is “a property of concepts.” It is the property of being instantiated.
Leaving aside the strange Analytic Philosopher commonplace of “instantiated concepts” (a Platonic muddling of the mode of knowing and being… And how does one “instantiate a concept“ anyway? Think about it real hard? Wait to hear a poofing noise?) It’s clear that this account of existence arises from seeing individuals as units “the number of X’s is one or more”… “The denial of the number nought”… The Analytic guys are noticing something real here, and I think it is more or less the same thing St. Thomas explains by the principle that matter is the principle of individuation. This principle in St. Thomas applies only so far as we see the individual in a way that it is seen in the “thin theory” of existence, that is, as a unit for counting. We can indeed see any of the things in nature this way, and to see them in this way is remarkably simple and elegant.
But there is more to the essence of the things around us than their matter, and so we need not merely consider them according to this mode of existence. For example, when I say that I appreciate and value my son as an individual, or when we speak of individual rights or even of an individual plant, the word individual isn’t being used to indicate the sort of existence that we experience when we look at the beads of an abacus, or count the numbers on an odometer. I’m not saying that “there is one or more” of my sons, or that rights belong to one or more persons, etc. Even if this is a fact, it is not what we mean to say. We simply can’t experience units of counting as anything but parts of a larger whole (even if there happens to only be one unit), but these other senses of individuality see the individual as existing for itself, that is, as separated from a larger whole. I speak of my son’s individuality because I want to speak of what sets him apart, what is uniquely his own, what is irreplaceable in him. This is a mode of individuation that is opposed to material individuation, even though it is obvious that my son is (also) essentially individuated materially.
Seen in this way, the “thin theory” of existence arises from the materiality of things, and the fact that their matter gives them a sort of individuation (a sort tied to number). But this is not the only mode of existence of the things around us, and it is not the only sort of individuality or being that we understand. It is, however, the first sort of existence or individuality that we understand, and is our first account of how things are essentially and universally.