The secret of avoiding monotony with the four-bar module was to vary the accent and the weight of the bars to avoid giving a similar emphatic accent … - Charles Rosen

The musical language which made the classical style possible is that of tonality, which was not a massive, immobile system but a living, gradually changing language from its beginning. It had reached a new and important turning point just before the style of Haydn and Mozart took shape.

Nevertheless, music will not acknowledge a context greater than itself—social, cultural, or biographical—to which it is conveniently subservient. To paraphrase Goethe's grandiose warning to the scientist: do not look behind the notes, they themselves are the doctrine.

I do not think that any composer has ever asked for octave glissandi on the black keys, but there is a recording by Moriz Rosenthal of Chopin's Black-Key Etude in which he plays the short octave passage in both hands glissando: it hurts my hands just to think about it.