We can imagine the Soul as a double light, a lesser corresponding to the soul proper, a purer representing its intellective phase; if now we suppose this intellective light equal to the light which is to be its object, we no longer distinguish between them; the two are recognised as one: we know, indeed, that there are two, but as we see them they have become one: this gives us the relation between the intellective subject and the object of intellection [in the duality and unity required by that primal intellection]: in our thought we have made the two into one; but on the other hand the one thing has become two, making itself into a duality at the moment of intellection, or, to be more exact, being dual by the fact of intellection and single by the fact that its intellectual object is itself. Enneads V,6,1
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. Enneads V,6,3