The theory of aesthetic senses, that is, of certain superior senses, such as sight and hearing, being the only ones for which aesthetic impressions exist, was debated as early as Plato. The _Hippias major_ contains a discussion upon this theme, which Socrates leads to the conclusion that there exist beautiful things, which do not reach us through impressions of eye or ear. But further than this, there exist things which please the eye, but not the ear, and _vice versa_; therefore the reason of beauty cannot be visibility or audibility, but something different from, yet common to both. Perhaps this question has never been so acutely and so seriously dealt with as in this Platonic dialogue. Home, Herder, Hegel, Diderot, Rousseau, Berkeley, all dealt with the problem, but in a more or less arbitrary manner. Herder, for instance, includes touch with the higher aesthetic senses, but Hegel removes it, as having immediate contact with matter as such, and with its immediate sensible qualities. Schleiermacher, with his wonted penetration, saw that the problem was not to be solved so easily. He refuted the distinction between clear and confused senses. He held that the superiority of sight and hearing over the other senses lay in their free activity, in their capacity of an activity proceeding from within, and able to create forms and sounds without receiving external impressions. The eye and the ear are not merely means of perception, for in that case there could be no visual and no auditive arts. They are also functions of voluntary movements, which fill the domain of the senses. Schleiermacher, however, considered that the difference was rather one of quantity, and that we should allow to the other senses a minimum of independence. The sensualists, as we know, maintain that all the senses are aesthetic. That is the hedonistic hypothesis, which has been dealt with and disproved in this book. We have shown the embarrassment in which the hedonists find themselves, when they have dubbed all the senses "aesthetic," or have been obliged to differentiate in an absurd manner some of the senses from the others. The only way out of the difficulty lies in abandoning the attempt to unite orders of facts so diverse as the representative form of the spirit and the conception of given physical organs or of a given material of impressions.