When Busoni was writing his "Sketch," Europe was still enraptured with the late Romantic works of Wagner, Liszt, et al. Tristan und Isolde was not quite half a century old and Richard Strauss' Elektra and Schoenberg's Gurrelieder had yet to reach the world. It was with these two works (particularly Elektra) that the Romantic era came to an end. So, when Busoni was putting to paper his aesthetic musings, composers had not yet come to face the hard problem of music in a post-Wagnerian age.
In this regard, Busoni's writings are ahead of there time.
It might not be coincidental that Schoenberg had started to eschew tonality a few short years after the publication of Busoni's book. Indeed, several passages in Sketch of a New Musical Aesthetic appear to be incredibly anticipatory of Schoenberg's own treatment of harmony.
Strange that one should feel major and minor as opposites. They both present the same face [...] and a mere touch of the brush suffices to turn the one into the other. The passage from either to the other is easy and imperceptible; when it occurs frequently and swiftly, the two being to shimmer and coalesce indistinguishably.--But when we recognize that major and minor form one Whole with a double meaning [...] we arrive unconstrainedly at the perception of the UNITY of our system of keys. The concept of "related" and "foreign keys vanish, and with them the entire intricate theory of degrees and relation. We possess one single key. [emphasis original]This can only be considered prophetic.
Busoni is also of the Objectivist school of musical though:
[...] [R]epresentation and description are not the nature of music; herewith we declare the invalidity of program music[...].In reality, program music is precisely as one-sided and limited as that which is called absolute. In place of architectonic and symmetric formulas, instead of the relation of Tonic and Dominant, it has bound itself in the stays of a connecting poetic--sometimes even philosophic--program.True, there are unequivocal descriptive effects of tone-painting (from these the entire principle took its rise+, but these means of expression are few and trivial, covering but a very small section of musical art. Begin with the most self-evident of all, the debasement of Tone to Noise in imitating the sounds of Nature--the rolling of thunder, the roar of forests, the cries of animals; then those somewhat less evident, symbolic--imitations of visual impressions, like the lightning-flash, springing movement, the flight of birds [...] These are auxiliaries, of which good use can be made upon a broad canvas, but which, taken by themselves, are no more to be called music than wax figures may pass for monuments. [emphasis added]
Busoni goes on to echo man of Hanslick's indictments of music as a means of expressing human emotions--that music cannot represent as object things which are essentially concepts.
This is somewhat puzzling to me as it seems outrightly contradictory to Busoni's thoughts in the very first chapter of his sketch:
Art-forms are the lasting, the more closely they adhere to the nature of their individual species of art, the purer they keep their essential ends.Sculpture relinquishes the expression of the human pupil, and effects of color; painting degenerates, when it forsakes the flat surfaces in depiction and takes on complexity in theatrical decoration or panoramic portrayal.Architecture has its fundamental form, growth from below upward, prescribed by static necessity; window and room necessarily provide the immediate and finishing configuration; these are eternal and inviolable requirements of the art.Poetry commands the abstract thought, which it clothes in words. More independant than the others, it reaches the furthest bounds.But all arts, resources and forms ever aim at one end, namely, the imitation of nature and the interpretation of human feelings. [emphasis original]
Strange. Not only is this contradictory, but Busoni never resolves this. If the goal of all art is to imitate and interpret human feelings, but music is impotent to do so, how precisely do we arrive at accomplishing this through music?
For this reason, it seems to me that Busoni has some interesting approaches to some of the problems of the aesthetics music--and has some very compelling and admirable prophesies!--but has little to offer the field as a whole. His music is great though!