3. We may be told that nothing prevents an identity being thus multiple. But there must be a unity underlying the aggregate: a manifold is impossible without a unity for its source or ground, or at least, failing some unity, related or unrelated. This unity must be numbered as first before all and can be apprehended only as solitary and self-existent.
When we recognize it, resident among the mass of things, our business is to see it for what it is- present to the items but essentially distinguished from them- and, while not denying it there, to seek this underly of all no longer as it appears in those other things but as it stands in its pure identity by itself. The identity resident in the rest of things is no doubt close to authentic identity but cannot be it; and, if the identity of unity is to be displayed beyond itself, it must also exist within itself alone.
It may be suggested that its existence takes substantial form only by its being resident among outside things: but, at this, it is itself no longer simplex nor could any coherence of manifolds occur. On the one hand things could take substantial existence only if they were in their own virtue simplex. On the other hand, failing a simplex, the aggregate of multiples is itself impossible: for the simplex individual thing could not exist if there were no simplex unity independent of the individual, [a principle of identity] and, not existing, much less could it enter into composition with any other such: it becomes impossible then for the compound universe, the aggregate of all, to exist; it would be the coming together of things that are not, things not merely lacking an identity of their own but utterly non-existent.
Once there is any manifold, there must be a precedent unity: since any intellection implies multiplicity in the intellective subject, the non-multiple must be without intellection; that non-multiple will be the First: intellection and the Intellectual-Principle must be characteristic of beings coming later.