Galen’s conception of ousia is complex and under-researched, involving a huge number of potentially relevant texts; his conception of dunamis is also subtle and difficult to summarize conclusively (see Hankinson 2014). One line of interpretation that seems plausible in relation to ousia is that its very homonymy is in fact significant for Galen’s metaphyics: that is to say, that although the Aristotelian sense of ousia is in principle distinct from the “everyday”, material one, there may be a tendency in Galen to elide the two usages, to conceive the answer to the question of something’s ousia in physical terms.