Voltaire and Rousseau were the heads of two important schools, and each of them set deep and unmistakable marks both on the opinion and the events of the century.

It would not be difficult to show that their influence was wider than that of the philosopher who discerned the inadequateness of both.

But Rousseau was moved by passion and sentiment; Voltaire was only the master of a brilliant and penetrating rationalism.

Diderot alone of this famous trio had in his mind the idea of scientific method; alone showed any feeling for a doctrine, and for large organic and constructive conceptions.

He had the rare faculty of true philosophic meditation.