The present volume contains a reprint of the preface and the first part of the Principles of Philosophy, together with selections from the second, third and fourth parts of that work, corresponding to the extracts in the French edition of Gamier, are also given, as well as an appendix containing part of Descartes' reply to the Second Objections (viz. , his formal demonstrations of the existence of Deity). The translation is based on the original Latin edition of the Principles, published in 1644.