in the first half.  His lively and many-sided receptivity, active industry, clever and combative eloquence, and enthusiastic disposition qualified him for this role beyond all his contemporaries, who testify that they owe even more to his stimulating conversation than to his writings.  He commenced by bringing Shaftesbury’s Inquiry into Virtue and Merit to the notice of his countrymen; and then turned his sword, on the one hand, against the atheists, to refute whom, he thought, a single glance into the microscope was sufficient, and, on the other, against the traditional belief in a God of anger and revenge, who takes pleasure in bathing in the tears of mankind.  Then followed a period of skepticism, which is well illustrated by the prayer in the Thoughts on the Interpretation of Nature, 1754:  O God!  I do not know whether thou art, but I will guide my thoughts and actions as though thou didst see me think and act, etc.  Under the influence of Holbach’s circle he finally reached (in the Conversation between D’Alembert and Diderot, and D’Alembert’s Dream, written in 1769, but not published until 1830, in vol. iv. of the Memoires, Correspondance, et Ouvrages Inedits de Diderot) the position of naturalistic monism—­there exists but one great individual, the All.  Though he had formerly distinguished thinking substance from material substance, and had based the immortality of the soul on the unity of sensation and the unity of the ego, he now makes sensation a universal and essential property of matter (la pierre sent), declares the talk about the simplicity of the soul metaphysico-theological nonsense, calls the brain a self-playing instrument, ridicules self-esteem, shame, and repentance as the absurd folly of a being that imputes to itself merit or demerit for necessary actions, and recognizes no other immortality than that of posthumous fame.  But even amid these extreme conclusions, his enthusiasm for virtue remains too intense to allow him to assent to the audacious theories of La Mettrie and Helvetius.

[Footnote 1:  Works in twenty-two vols., Paris, Briere, 1821; latest edition, 1875 seq.  Cf. on Diderot the fine work by Karl Rosenkranz, Diderots Leben und Werke, 1866.]

French natural science also tended toward materialism.  Buffon (Natural History, 1749 seq) endeavors to facilitate the mechanical explanation of the phenomena of life by the assumption of living molecules, from which visible organisms are built up.  Robinet (On Nature, 1761 seq.), availing himself of Spinozistic and Leibnitzian conceptions, goes still further, in that he endows every particle of matter with sensation, looks on the whole world as a succession of living beings with increasing mentality, and subjects the interaction of the material and psychical sides of the individual, as well as the relation of pleasure and pain in the universe, to a law of harmonious compensation.