I examine Alexander of Aphrodisias’ theory of action, addressing the question how his view that human actions are determined by reason accounts for the capacity of doing otherwise. Calling into question the standard view that Alexander frees agents from internal determination, I argue that (1) the capacity of doing otherwise is a consequence of determination by reason, since it enables agents to do something different from what they would have done had they followed external circumstances; and (2) this capacity is (...) compatible with causal determination by reason because as a case of potentiality for opposites, it grants agents the qualified possibility of doing otherwise insofar as their nature as human beings is concerned – a possibility which remains also when their actions are causally determined by reason and by their internal disposition. I show further that these elements of Alexander’s theory of action are ultimately based on his conception of the soul, specifically on his commitment to Aristotle’s view that the human soul is not purely rational, as the Stoics hold, but has nonrational and rational parts. (shrink)