Full Idea
Questions of conduct do not fall under any art or professional tradition, but the agents are compelled at every step to think out for themselves what the circumstances demand, just as happens in the arts of medicine and navigation.
Gist of Idea
There is no fixed art of good conduct, and each situation is different, as in navigation
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1104a08)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.93
A Reaction
It is interesting that some areas of medicine, and a lot of navigation, have become much more precise in modern times. His thought sounds pessimistic, but it is a lynchpin of virtue theory. 'Have the right disposition, then attend to the details'.