Built out of his own sensations:  for the philosophy of Locke was now triumphant in France.  I have used the term Cartesianism to designate, not the metaphysical doctrines of Descartes (innate ideas, two substances, and the rest), but the great principles which survived the passing of his metaphysical system—­the supremacy of reason, and the immutability of natural laws, not subject to providential interventions.  These principles still controlled thought, but the particular views of Descartes on mental phenomena were superseded in France by the psychology of Locke, whose influence was established by Voltaire and Condillac.  The doctrine that all our ideas are derived from the senses lay at the root of the whole theory of man and society, in the light of which the revolutionary thinkers, Diderot, Helvetius, and their fellows, criticised the existing order and exposed the reigning prejudices.  This sensationalism (which went beyond what Locke himself had really meant) involved the strict relativity of knowledge and led at once to the old pragmatic doctrine of Protagoras, that man is the measure of all things.  And the spirit of the French philosophers of the eighteenth century was distinctly pragmatic.  The advantage of man was their principle, and the value of speculation was judged by its definite service to humanity.  “The value and rights of truth are founded on its utility,” which is “the unique measure of man’s judgements,” one thinker asserts; another declares that “the useful circumscribes everything,” l’utile circonscrit tout; another lays down that “to be virtuous is to be useful; to be vicious is to be useless or harmful; that is the sum of morality.”  Helvetius, anticipating Bentham, works out the theory that utility is the only possible basis of ethics.  Bacon, the utilitarian, was extolled like Locke. [Footnote:  The passages quoted on utility are from d’Holbach, Systems de la nature, i. c. 12, p. 224; c. 15, p. 312; Diderot, De I’interpretation de la nature in OEuvres, ii. p. 13; Raynal, Histoire des deux Indes, vii. p. 416.  The effectiveness of the teaching may be illustrated from the Essay on Man, by Antoine Rivarol, whom Burke called the Tacitus of the Revolution.  “The virtues are only virtues because they are useful to the human race.”  OEuvres choisis (ed. de Lescure), i. p. 211.] As, a hundred years before, his influence had inspired the foundation of the Royal Society, so now his name was invoked by the founders of the Encyclopaedia. [Footnote:  See d’Alembert’s tribute to him in the Discours preliminaire.]

Beneath all philosophical speculation there is an undercurrent of emotion, and in the French philosophers of the eighteenth century this emotional force was strong and even violent.  They aimed at practical results.  Their work was a calculated campaign to transform the principles and the spirit of governments and to destroy sacerdotalism.  The problem for the human race being to reach a state of felicity