Objection IV, then, presents us with a powerful argument against the bundle theory of substance. Since it is possible for different substances to be qualitatively indiscernible, the bundle theorist’s attempt to construe substances as wholes whose constituents are exclusively properties breaks down. But Objection IV is not meant merely as a refutation of the bundle theory; as we saw in Chapter Six, it presents itself as well as an argument establishing the inescapability of a substratum ontology. It should now be clear how the objection can play that role. The Principle of Constituent Identity tells us that indiscernibility with respect to constituents entails numerical identity; but, then, since it is possible for different substances to be indiscernible with respect to their pure properties, each substance must incorporate a constituent over and above its pure properties. Since, however, the aim is to specify the constituents out of which substances are composed, the additional entity cannot be anything which presupposes the wholes that are substances; it cannot, then, be an impure property. But since we have set the properties of a substance (both pure and impure) on the one side and this additional entity on the other, the constituent of a substance that guarantees its individuation must be something such that its existence is independent of the properties with which it is co-present; its being whatever it is cannot involve any of those properties.
KeywordsNumerical Diversity Bare Substratum Substratum Theorist Ordinary Object Bundle Theory
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