In either case, different ousiai are items that are definitionally different, different types of thing, not just qualitatively different versions or sub-categories of one thing. A relevant example is that of the three parts of the Platonic tripartite soul. Although typically referred to as different capacities (dunameis), it is more correct to state that they are three different substances (ousiai)—partly because, in fact, each one of them itself has a number of capacities (PHP VI.3, 374–5; cf. QAM 2, 377 and 4, 386). And, as we have seen, the notion of a change “in the whole substance” as opposed to a mere change in qualities is an important one in Galen’s physics; this gives an account of one type of thing’s turning into another.