It should be evident that such empirical collections are not reducible to science. They are composed of notions, taken from various sciences and disciplines, and their philosophical and scientific principles are to be found in the latter. To propose to construct a scientific theory of the different arts would be to wish to reduce to the single and homogeneous what is by nature multiple and heterogeneous; to wish to destroy the existence as a collection of what was put together precisely to form a collection. Were we to try to give scientific form to the manuals of the architect, the painter, or the musician, it is clear that nothing would remain in our hands but the general principles of Mechanics, Optics, or Acoustics. And if we were to extract and isolate what may be scattered among them of properly artistic observations, to make of them a scientific system, then the sphere of the individual art would be abandoned and that of Æsthetic entered, for Æsthetic is always general Æsthetic, or rather it cannot be divided into general and special. This last case (that is, the attempt to furnish a technique which ends in composing an Æsthetic) arises when men possessing strong scientific instincts and a natural tendency to philosophy set themselves to work to produce such theories and technical manuals. [Sidenote: _Criticism of æsthetic theories of particular arts_.] But the confusion between Physics and Æsthetic has attained to its highest degree, when æsthetic theories of particular arts are imagined, to answer such questions as: What are the _limits_ of each art? What can be represented with colours, and what with sounds? What with simple monochromatic lines and what with touches of various colours? What with tones, and what with metres and rhythms? What are the limits between the figurative and the auditive arts, between painting and sculpture, poetry and music? This, translated into scientific language, is tantamount to asking: What is the connexion between Acoustics and æsthetic expression? What between the latter and Optics?--and the like. Now, if _there is no passage_ from the physical fact to the æsthetic, how could there be from the æsthetic to particular groups of physical facts, such as the phenomena of Optics or of Acoustics? [Sidenote: _Criticism of the classification of the arts._] The so-called _arts_ have no æsthetic limits, because, in order to have them, they would need to have also æsthetic existence in their particularity; and we have demonstrated the altogether empirical genesis of those partitions. Consequently, any attempt at an æsthetic classification of the arts is absurd. If they be without limits, they are not exactly determinable, and consequently cannot be philosophically classified. All the books dealing with classifications and systems of the arts could be burned without any loss whatever. (We say this with the utmost respect to the writers who have expended their labours upon them.)