Moving back and forth between the history of philosophy and the contributions of philosophers in his own day, Durkheim takes up topics as diverse as philosophical psychology, logic, ethics, and metaphysics, and seeks to articulate a unified philosophical position. Remarkably, the ‘social realism’ that is so characteristic of his later work – where he insists, famously, that social facts cannot be reduced to psychological or economic ones, and that such facts constrain human action in important ways – is totally absent in these early lectures. For this reason, they will be of special interest to students of the history of the social sciences, for they shed important light on the course of Durkheim’s intellectual development. Intellectual historians, historically-minded philosophers, and French historians will all find the lectures a valuable historical document. Insofar as they speak to the philosophical foundations of Durkheim’s thought, they should also be of great interest to social theorists.