In Book K of the Metaphysics Aristotle raises a problem about a very persistent concern of Greek philosophy, that of the relation between the one and the many , but in a rather peculiar context. He asks: ‘What on earth is it in virtùe of which mathematical magnitudes are one? It is reasonable that things around us [i.e. sensible things] be one in virtue of [their] ψνχ or part of their ψνχ, or something else; otherwise there is not one but (...) many, the thing is divided up. But [mathematical] objects are divisible and quantitative. What is it that makes them one and holds them together?’. (shrink)