Maine de Biran's work has had an enormous influence on the development of French Philosophy – Henri Bergson called him the greatest French metaphysician since Descartes and Malebranche, Jules Lachelier referred to him as the French Kant, and Royer-Collard called him simply 'the master of us all' – and yet the philosopher and his work remain unknown to many English speaking readers. From Ravaisson and Bergson, through to the phenomenology of major figures such as Maurice Merleau-Ponty, Michel Henry, and Paul Ricoeur, Biran's influence is evident and acknowledged as a major contribution. The notion of corps propre, so important to phenomenology in the twentieth century, originates in his thought. His work also had a huge impact on the distinction between the virtual and the actual as well as the concepts of effort and puissance, enormously important to the development of Deleuze's and Foucault's work. This volume, the first English translation of Maine de Biran in nearly a century, introduces Anglophone readers to the work of this seminal thinker. The Relationship Between the Physical and the Moral in Man is an expression of Biran's mature 'spiritualism' and philosophy of the will as well as perhaps the clearest articulation of his understanding of what would later come to be called the mind-body problem. In this text Biran sets out forcefully his case for the autonomy of mental or spiritual life against the reductive explanatory power of the physicalist natural sciences. The translation is accompanied by critical essays from experts in France and the United Kingdom, situating Biran's work and its reception in its proper historical and intellectual context.