Claude Perrault’s Essais de Physique1 were published in two parts in 1680 and 1688, an important time for the spread of Cartesianism in France. Perrault himself espoused a form of mechanism in physics, and put forward mechanical accounts of gravity and cohesion. He even wrote of the mechanism of animals.2 Nevertheless, in his physiological writings Perrault revealed himself as an antagonist of the Cartesian theory of the mind or soul. Indeed, while he never directly identified his opponents, his discussions of the soul systematically criticise the doctrines of Descartes and followers such as Malebranche. By studying Perrault’s ideas on the soul, we not only become acquainted with a curious historical alternative to the Cartesian theory, but we also can develop a clear idea of what appeared controversial in that theory to an important contemporary. The result is that the Cartesian theory of mind takes on a very different look than it does from the perspective of the twentieth century.