Aristotle’s doctrine of voluntary actions differs as it is examined in the Eudemian and in the Nicomachean Ethics. For in the first, but not in the second, it displays as one of its conditions that the agent can not to do what she is about to do, and consequently voluntariness is put under the heading of what depends on thought. In the Nicomachean Ethics, however, this condition no more characterizes voluntariness, and the reference to what depends on thought is dropped out of the text. The main target of this paper is to elucidate this difference; some comments are also made to De motu animalium 11.