Aristotle and the Problem of Moral Responsibility: Pre-determinism or Indeterminism?

When discusses the voluntary acts, in EN III 1-5, Aristotle deals with two questions: (i) under which conditions someone can be morally responsible for his actions and (ii) when someone can be seen as free to act. Aristotle argues that we can be morally responsible only if is in our power to act and also it is in our power not to act. The aim of this essay is to analyze (i) and (ii), considering if the concept of "in our power" is used by Aristotle in an indeterminist or pre-determinist sense. It will be defended that there are textual references in favor of both interpretations, from which we can conclude that the question is unsolvable.