The Traite des systemes is a milestone in the intellectual history of the eighteenth century. This is a study of its content, structure, sources and importance. It includes a discussion of Condillac's analysis of good and bad systems, the adequacy of his knowledge and under standing of the speculative metaphysics of the preceding century, the effectiveness of his method of attack on seventeenth-century metaphysical systems, his conception of empirical and scientific method, and in particular his understanding of the role of hypotheses, his application of the Newtonian scientific method to...