Secondly: since they treat the Substrate as one thing, they do not enumerate the Existents; they look instead for principles of the Existents. There is however a difference between speaking of the actual Existents and of their principles.
If Matter is taken to be the only Existent, and all other things as modifications of Matter, it is not legitimate to set up a single genus to embrace both the Existent and the other things; consistency requires that Being [Substance] be distinguished from its modifications and that these modifications be duly classified.
Even the distinction which this theory makes between Substrates and the rest of things is questionable. The Substrate is [necessarily] one thing and admits of no differentia — except perhaps in so far as it is split up like one mass into its various parts; and yet not even so, since the notion of Being implies continuity: it would be better, therefore, to speak of the Substrate, in the singular.
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