Full Idea
In every case a man stops inquiring how to act when he has traced the starting-point of action back to himself, i.e. to the dominant part of himself; for it is this that makes the choice.
Gist of Idea
Deliberation ends when the starting-point of an action is traced back to the dominant part of the self
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1113a06)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.120
A Reaction
A footnote says the 'dominant part' of the soul is reason. If we dispense with 'free will' (and we should), this is the core of moral responsibility. Responsible actions are those caused by the dominant part of the mind.