  In the passage of Proclus’ Parmenides commentary cited above there appears a passage dealing with a view that makes the participants in an Idea ‘aim for’ that Idea, which in turn aims for that which ‘comes before’ it, which must be the One. So Xenocrates looks to be the source for the ‘bizarre’ demonstration, and if so he is invoking final causality in relating the forms (which are formal numbers) to the One. Aristotle himself has the heavenly spheres move as they do out of a desire to emulate the unmoved mover (Metaphysics XII 7. 1072a26-b4), and even says that the matter in a form/matter compound ‘aims at’ its form (Physics I 9. 192a16–25), so this use of final causality was, one supposes, Academic. But about Xenocrates’ ‘demonstration’ Aristotle is merciless: “one should … not without reason give any credit at all to things it is not easy to believe even with reason”.