Plotinos: Complete Works, v. 3 In Chronological Order,...

Consequently, in speaking of (beings) other than (essence itself), as, for instance, of man, we say simply "man" (without adding to it the idea of unity312); if however we say "a man," it is to distinguish him from two; if however we use the word one in still another sense, it is by adding to it "some" (as, "someone"). Not so is it with essence; we say, "being one," conceiving of "being" ("essence") and one, as if forming a single whole, and in positing essence as one, we emphasize its narrow affinity with the Good. Thus conceived, essence becomes one;313 and in the one finds its origin and goal. Nevertheless it is not one as unity itself, but rather in a different manner, in this sense that the (unity of essence) admits priority and posteriority. What then is (the unity of essence)? Must it not then be considered similar in all the parts (of essence), as something common to all (and consequently, as forming a genus)? But in the first place, the point is also something common to all the lines, and nevertheless it is not a genus; in the numbers, unity is something common to all, and is not any more of a genus. Indeed, the unity which is found in the monad, in the dyad (or pair), and in other numbers, cannot be confused with unity in itself. Then, nothing hinders there being in essence some anterior, and other posterior parts, both simple and compound ones (which would be impossible for the One in itself).