But M. Guyau is the most important of sociological aestheticians. His works, published in Paris toward the end of last century, and his posthumous work, entitled _Les problèmes de l'Esthétique contemporaine_, substitute for the theory of play, that of _life_, and the posthumous work above-mentioned makes it evident that by life he means social life. Art is the development of social sympathy, but the whole of art does not enter into sociology. Art has two objects; the production of agreeable sensations (colours, sounds, etc.) and of phenomena of psychological induction, which include ideas and feelings of a more complex nature than the foregoing, such as sympathy for the personages represented, interest, piety, indignation, etc. Thus art becomes the expression of life. Hence arise two tendencies: one for harmony, consonance, for all that delights the ear and eye; the other transforming life, under the dominion of art. True genius is destined to balance these two tendencies; but the decadent and the unbalanced deprive art of its sympathetic end, setting aesthetic sympathy against human sympathy. If we translate this language into that with which we are by this time quite familiar, we shall see that Guyau admits an art that is merely hedonistic, and places above it another art, also hedonistic, but serving the ends of morality. M. Nordau wages war against the decadent and unbalanced, in much the same manner as Guyau. He assigns to art the function of re-establishing the integrity of life, so much broken up and specialized in our industrial civilization. He remarks that there is such a thing as art for art's sake, the simple expression of the internal states of the individual, but it is the art of the cave-dweller. C. Lombroso's theory of genius as degeneration may be grouped with the naturalistic theories. His argument is in essence the following. Great mental efforts, and total absorption in one dominant thought, often produce physiological disorders or atrophy of important vital functions. Now these disorders often lead to madness; therefore, genius may be identified with madness. This proof, from the particular to the general, does not follow that of traditional Logic. But with Lombroso, Büchner, Nordau, and the like we have come to the boundary between specious and vulgar error. They confuse scientific analysis with historical research. Such inquiries may have value for history, but they have none for Aesthetic. Thus, too, A. Lang maintains that the doctrine of the origin of art as disinterested expression of the mimetic faculty is not confirmed in what we know of primitive art, which is rather decorative than expressive. But primitive art, which is a given fact to be interpreted, cannot ever become its own criterion of interpretation. The naturalistic misunderstanding has had a bad effect on linguistic researches, which have not been carried out on the lofty plane to which Humboldt and Steinthal had brought them.