Professor Lévy-Bruhl followed up his _History of Modern Philosophy in France_ by a substantial work on the philosophy of Auguste Comte. It forms a volume of the _Bibliothèque de Philosophie Contemporaine_, which has already devoted four other works to the Positive Philosophy. It is as well to premise that this treatise dealt solely with the _philosophy_, not with the polity, or any part of the religious scheme of Comte. Professor Lévy-Bruhl writes as a student, but not as an adherent of Auguste Comte. His entire work is rather an exposition, not a refutation, or a criticism, or an advocacy of Comte’s philosophical system. But it may be said at once that no one abroad or at home, certainly neither Mill, nor Lewes, nor Spencer, nor Caird, has so truly grasped and assimilated Comte’s ideas as M. Lévy-Bruhl has done. In his _Introduction_ M. Lévy-Bruhl very clearly states the scope of his work, and his own general attitude. He traces the origin of Comte’s philosophy in the mental effervescence of the first generation of the present century towards a reorganisation of society, after the upheaval left by the Revolution and its consequences. He correctly states the relation of St. Simon to Comte as being that of an initial stimulus. The cardinal difference between Comte and all the socialists and founders of social and religious Utopias consisted in this, that Comte saw the necessity of a new system of philosophy as the indispensable preliminary to any reorganisation of society. In 1824, at the age of twenty-six, Comte wrote:—“Discussions about institutions are pure folly until the spiritual reconstitution of society is effected or much advanced.” The construction of an intellectual reorganisation, before any social restoration was possible, occupied twenty or thirty years of Comte’s life. And when he opened his _Polity_, or social and religious scheme, the conditions had much changed: the public and its interests were no longer what they had been in 1820-30. M. Lévy-Bruhl effectively disposes of the objection of Littré, to which Mill gave countenance, that the _Polity_, with the whole of Comte’s second or social system, was in contradiction with his first and philosophic system as propounded in the _Philosophy_. As M. Lévy-Bruhl proves, the six _Opuscules_ dating from 1819 to 1826, some years before the _Cours_, which only began in 1830 and occupied twelve years, contain in germ the scheme ultimately elaborated in the _Politique_, from 1851 to 1854. Besides this, the _Letters to Mill_, which M. Lévy-Bruhl edited in 1899, and the _Letters to Valat_, which are long antecedent to the _Politique_, show the same governing design. To the unity of Comte’s doctrine M. Lévy-Bruhl bears emphatic testimony:— “His whole life was the methodical execution of his programme.... He had but one system, not two. From the _Opuscules_ of his twentieth year, to the _Synthèse_ of his last year, it is the development of one and the same conception.”