 The level of numbers comes about when the second principle, plurality, kicks in. One of the more confusing things about this level is that Speusippus seems to have supposed that among the numbers was the number 1: in this he was apparently ahead of his time, for the generally accepted view was that 1 is not a number (for this see Aristotle, Metaphysics, book X, Euclid, Elements vii def. 2, proof of prop. 1, et passim). That Speusippus accepted the number 1 follows from the mathematics of the one extensive fragment of his work that we have: a quotation preserved in pseudo-Iamblichus, Theologumena arithmeticae (see below). But if this is so, it is essential to recall that we are dealing with Aristotle’s ‘mathematical’ numbers, where there is a plurality for each number. So there is a plurality of numbers 1 (so that we can add 1 and 1 to get 2, etc.). Then the One is not the number 1; the latter comes about when you get a plurality of units, any of which counts as a 1, any couple of which counts as a 2, and so on. That the One is not the number 1 is only what we should expect, given the Principle of Alien Causality: the principle for numbers is not itself a number.