An important facet of the European philosophical tradition is represented most clearly and characteristically by a group of French philosophers of the eighteenth century. The group contains some of the most famous names in French literature and includes, among others, La Mettrie, Voltaire, Diderot, d’Alembert, and d’Holbach. These writers cannot be said to form a philosophical school, nor were they all philosophers in the modern sense of the word. Some, like Voltaire and Diderot, were literary men; some, like d’Alembert, scientists and mathematicians. But each in his own way gave expression to a certain characteristic point of view that may be called the syndrome of progressive thought. We shall first take a general survey of this syndrome and then consider in more detail one particular manifestation of itthe work of d’Holbach.