I argue that the debate between proponents of substance causation and proponents of causation by powers, as to whether substances or their powers are causes, hinges on whether or not powers (as properties) are self-exemplifying or non-self-exemplifying properties. Substance causation is committed to powers being non-self-exemplifying properties while causation by powers is committed to powers being self-exemplifying properties. I then argue that powers are non-self-exemplifying properties, in support of substance causation.