1713-1784. French encyclopedist and key figure of the Enlightenment* philosophy. Born in Langres, son of a master-cutler, he studied in local Jesuit schools and at the College of Louis le Grand, Paris, receiving his master's degree (1732). He married his secretary in 1743. After translating English works, he published a defense of natural religion, Pensées philosophiques (1746). He became editor-in- chief of the Encyclopédie, which monumental enterprise was his chief occupation until its completion in 1772. In 1749 he was imprisoned briefly because of his Lettre sur les aveugles which questioned the existence of purpose in the universe. The encyclopedia was officially suspended in 1759 because of its advanced ideas, but was published clandestinely. He traveled in Russia (1773-74), meeting Catherine the Great, who purchased his library, paying him in advance to provide his daughter's dowry. His closing years were spent in semiretirement in France. Many of his writings were published posthumously.