Full Idea
Morally fine and just conduct…involves so much difference and variety that they are widely believed to be such only by convention and not by nature.
Clarification
'Convention' is the Greek word 'nomos', which also translates as 'law'
Gist of Idea
Moral acts are so varied that they must be convention, not nature
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1094b14)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.65
A Reaction
Relativists about morality do typically point to the very diverse standards in different cultures. Critics can point to the huge similarities, when basic human issues are concerned.