Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Perhaps then it will be as well to specify the nature and number of these circumstances. They are （1） the agent, （2） the act, （3） the thing¹ that is affected by or is the sphere of² the act; and sometimes also （4） the instrument, for instance, a tool with which the act is done, （5） the effect, for instance, saving a man's life, and （6） the manner, for instance, gently or violently.1. [17]

Now no one, unless mad, could be ignorant of all these circumstances together; nor yet, obviously, of （l） the agent—for a man must know who he is himself. But a man may be ignorant of （2） what he is doing, as for instance when people say ‘it slipped out while they were speaking,’ or ‘they were not aware that the matter was a secret,’ as Aeschylus said of the Mysteries³; or that ‘they let it off when they only meant to show how it worked’ as the prisoner pleaded in the catapult case. Again （3） a person might mistake his son for an enemy, as Merope does⁴; or （4） mistake a sharp spear for one with a button on it, or a heavy stone for a pumice-stone; or （5） one might kill a man by giving him medicine with the intention of saving his life; or （6） in loose wrestling⁵ hit him a blow when meaning only to grip his hand. 1. [18] Ignorance therefore being possible in respect of all these circumstances of the act, one who has acted in ignorance of any of them is held to have acted involuntarily, and especially so if ignorant of the most important of them; and the most important of the circumstances seem to be the nature of the act itself and the effect it will produce.1. [19]

Such then is the nature of the ignorance that justifies our speaking of an act as involuntary,