This article has for its object the more clearly defining one of the theses sustained by the author in his work, Formes élémentaires de la Vie Religieuse, namely, the possibility of explaining scientifically the constitutional dualism of man. Religions have always recognised this quality, regarding man as formed of two beings radically different—the soul on the one side, the body on the other. Psychological analysis, in a sense, confirms this belief. There are sensations and sensual tendencies on the one side, thought and moral activity on the other.