Full Idea
Though an appeal to general opinion may justly, in the speculative sciences of metaphysics, natural philosophy or astronomy, be deemed unfair, yet in all questions with regard to morals there is really no other standard for deciding controversies.
Gist of Idea
Moral questions can only be decided by common opinion
Source
David Hume (Of the original contract [1741], p.291)
Book Reference
Hume,David: 'Selected Essays' [OUP 1996], p.291
A Reaction
Surely this is too pessimistic. Common opinion decided to burn people to death for being witches. Common opinion may usually win, but there must sometimes be good grounds for resisting it.