We are constantly railing against the passions; we ascribe to them all of man's afflictions, and we forget that they are also the source of all his pleasures … But what provokes me is that only their adverse side is considered … and yet only passions, and great passions, can raise the soul to great things. Without them there is no sublimity, either in morals or in creativity. Art returns to infancy, and virtue becomes small-minded.

As translated in Diderot (1977) by Otis Fellows, p. 39 - Pensées Philosophiques (1746)