Writers begin by seeking the rules on which, for the common utility, it would be appropriate for men to agree among themselves; they then give the name of 'natural law' to these rules, with no other proof than their presumed good results.
Gist of Idea
Writers just propose natural law as the likely useful agreements among people
Jean-Jacques Rousseau (Discourse on the Origin of Inequality , Pref)
The arguments for natural law strike me as quite good, but pinning down its content looks incredibly elusive, and at the mercy of cultural influences.
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.35