 It may help a little, but not a lot, to notice that Xenocrates makes (see below) the soul is a self-moving number.  In any case, the resulting position is possibly quite unstable: Aristotle certainly thinks so. For Plato and Speusippus, the addition of 2 and 3 is a matter of putting together a group of units that is a mathematical 2 with a disjoint group of units that is a mathematical 3 (that numbers are such collections of units is a view that can still be found later, perhaps most importantly, given his influence, in Euclid, Elements VII def. 2). Aristotle, too, understood addition in this way, although with a completely different take on the underlying ontology. We do not know how Xenocrates understood addition: perhaps as a sort of map telling you that if you are on the unique formal number 2 and you want to add the unique formal number 3 to it, you cannot, strictly speaking, do that, but taking three steps on in the series will get you to the unique formal number 5, and that is what ‘2 + 3 = 5’ really means. There is, as far as I know, no evidence to support this conjecture, but it has the advantage of explaining Aristotle’s complaint, voiced more than once in the passages cited (see 1080b28–30, 1083b4–6, 1086a9–11), that Xenocrates actually makes doing mathematics impossible: he ends up destroying mathematical number, and if the above guess should be correct about Xenocrates’ handling of addition, it is readily seen how someone of Aristotle’s persuasion might think that Xenocrates is not so much explaining addition as explaining it away.