Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[3] By a voluntary action, as has been said before,¹ I mean any action within the agent's own control which he performs knowingly, that is, without being in ignorance of the person affected, the instrument employed, and the result （for example, he must know whom he strikes, and with what weapon, and the effect of the blow）; and in each of these respects both accident² and compulsion must be excluded. For instance, if A took hold of B's hand and with it struck C, B would not be a voluntary agent, since the act would not be in his own control. Or again, a man may strike his father without knowing that it is his father, though aware that he is striking some person, and perhaps that it is one or other of the persons present³; and ignorance may be similarly defined with reference to the result, and to the circumstances of the action generally. An involuntary act is therefore an act done in ignorance, or else one that though not done in ignorance is not in the agent's control, or is done under compulsion; since there are many natural processes too that we perform or undergo knowingly, though none of them is either voluntary or involuntary⁴; for example, growing old, and dying.