This paper examines Aristotle’s notion of priority with the specific aim of capturing the sort of priority that characterizes the primacy of substances in his metaphysics. I reject the traditional interpretation, which understands the ontological priority of substances in terms of independent existence. But there are rather two sorts of priority: the ontological priority of substances should be understood in terms of completeness, whereas the ontological priority of “substances-of-something” (the essences) is a causal-explanatory priority. Furthermore, an important piece of Aristotle’s (...) argument against Platonism is that these two sorts of priority – namely, the completeness priority and the causal-explanatory priority – should be kept distinct. (shrink)