Philosophers have tended to suppose that a computational theory of the mind would need to be a version of functionalism, and so that it would treat mental entities as being metaphysically on a par with the entities that are defined by their role in some functional organization. This is a mistake. Computational theories can make use of a much larger metaphysical repertoire (and doing so liberates them from a number of confusions). We can bring some hitherto neglected parts of this repertoire into view by taking an Aristotelian approach to the metaphysics of computation. This talk takes some preliminary steps towards doing so, focussing in particular on Aristotle’s distinctions between substantial and accidental being, and between capacities and activities.