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

Unity (may mean two things). The absolute Unity, to which nothing may be added, neither Soul, nor Intelligence, nor anything else, cannot be predicated as attribute of anything, and therefore cannot be a genus. But if we are referring to the unity which we attribute to essence, when we say that essence is one, it is no longer the original Unity. Besides, how could the absolute One, which within itself admits of no difference, beget species? If it cannot do this, it cannot be a genus. How indeed could you divide unity? By dividing it, you would multiply it; and thus Unity-in-itself would be manifold, and in aspiring to become a genus it would annihilate itself. Besides, in order to divide this unity into species, you would have to add something to unity, because it does not contain differences such as exist in being. Intelligence might well admit differences between essences, but this could not possibly be the case with unity. The moment you add a single difference, you posit duality, and consequently destroy unity; for everywhere the addition of a single unity causes any previously posited number to disappear.