 Simplicius, in his commentary on Aristotle’s Categories (Kalbfleisch 1907, 63.21–24) tells us that Xenocrates objected to Aristotle’s list of ten categories as too long: he thought all that was needed was the distinction, visible in Plato, between things that are ‘by virtue of themselves’ and things that are ‘relative to something’ (see, e.g., Sophist 255c, and Dancy 1999). The standard examples help clarify this: the terms man and horse are of the first sort, whereas large, relative to small, good relative to bad, etc., are of the latter type.