[Footnote 1: Of the many treatises on the philosophy of Descartes those of C. Schaarschmidt (_Descartes und Spinoza_, 1850) and J.H. Löwe, 1855, may be mentioned. Further, M. Heinze has discussed _Die Sittenlehre des Descartes_, 1872; Ed. Grimm, _Descartes' Lehre von den angeborenen Ideen_, 1873; G. Glogau, _Darlegung und Kritik des Grundgedankens der Cartesianisch. Metaphysik (Zeitschrift für Philosophie_, vol. lxxiii. p. 209 _seq_.), 1878; Paul Natorp, _Descartes' Erkenntnisstheorie_, 1882; and Kas. Twardowski, _Idee und Perception_ in Descartes, 1892. In French, Francisque Bouillier (_Histoire de la Philosophie Cartésienne_, 1854) and E. Saisset (_Précurseurs et Disciples de Descartes_, 1862) have written on Cartesianism. [The _Method, Meditations, and Selections from the Principles_ have been translated into English by John Veitch, 5th ed., 1879, and others since; and H.A.P. Torrey has published _The Philosophy of Descartes in Extracts from his Writings_, 1892 (Sneath's Modern Philosophers). The English reader may be referred, also, to Mahaffy's _Descartes_, 1880, in Blackwood's Philosophical Classics; to the article "Cartesianism," _Encyclopedia Britannica_, 9th ed., vol. v., by Edward Caird; and, for a complete discussion, to the English translation of Fischer's _Descartes and his School_' by J.P. Gordy, 1887.--TR.]] We begin our discussion with Descartes's noëtical and metaphysical principles, and then take up in order his doctrine of nature and of man. %1. The Principles%.