This volume collects the writings of French philosopher and psychologist Ignace Meyerson, spanning from 1920 to 1983. A key figure in the history of psychology and the philosophy of mind, Meyerson's work explores the nature of psychological functions, the role of language in thought, and the historical development of scientific ideas. The collection includes essays, lectures, and previously unpublished material that reflect his interdisciplinary approach, bridging philosophy, psychology, and the history of science. Published posthumously by Presses Universitaires de France, this compilation offers a comprehensive overview of Meyerson's intellectual trajectory and his contributions to understanding the human mind within its cultural and historical context.