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

In what sense does the number which is within us (before we enumerate) have a mode (of existence) other (than the one we produce in enumeration)? Because it is the number constitutive of our being, which, as Plato says,40 participates in number and harmony, and is a number and harmony; for the soul is said to be neither a body nor an extension; she therefore is a number, since she is a being. The number of the body is a being of the same nature as the body; the number of the soul consists in the beings which are incorporeal like souls. Then, for the intelligible entities, if the animal itself be plurality, if it be a triad, the triad that exists in the animal is essential. As to the triad which subsists, not in the animal, but in essence, it is the principle of being. If you enumerate the animal and the beautiful, each of these two in itself is a unity; but (in enumerating them), you beget number in yourself, and you conceive a certain quantity, the pair. If (like the Pythagoreans) you say that virtue is a group of four, or tetrad, it is one so far as its parts (justice, prudence, courage, and temperance) contribute to the formation of a unity; you may add that this group of four, or tetrad, is a unity, so far as it is a kind of substrate; as to you, you connect this tetrad with the one that is inside of you.41