Full Idea
Diderot is among the first to preach that there are two men: the artificial man, who belongs in society and seeks to please, and the violent, bold, criminal instinct of a man who wishes to break out (and, if controlled, is responsible for works of genius.
Gist of Idea
There are two sides to men - the pleasantly social, and the violent and creative
Source
report of Denis Diderot (works [1769], Ch.3) by Isaiah Berlin - The Roots of Romanticism
Book Reference
Berlin,Isaiah: 'The Roots of Romanticism' [Pimlico 2000], p.51
A Reaction
This has an obvious ancestor in Plato's picture (esp. in 'Phaedrus') of the two conflicting sides to the psuché, which seem to be reason and emotion. In Diderot, though, the suppressed man has virtues, which Plato would deny.