Bach And The Transcending Of The Immediately Audible

[T]he existence of musical significance which transcends the immediate audible experience is essential to Bach's style. I do not imply anything mystical, or anything that is beyond our ordinary experience of music; only that some of the most important forces in the development — the actual movement through time — of a work of Bach are latent in its material without becoming audible until the moment that he chooses to make them so. The forces shaping the movement of a work by Beethoven or Mozart are far more immediately audible. The dissonance in the seventh bar of the Eroica audibly implies the modulation to F major that Beethoven only makes when he repeats the passage hundreds of bars later; the movement to G-flat major in the slow movement of Mozart's G minor Symphony begins in the second bar. The material of the great classical [period] composers is directional — we can hear the opening of the Eroica moving towards something, even if we cannot name it, and its arrival, presented as a surprise, is also a logical satisfying of a dynamic tonal impulse, the resolution of a tension. But if what is to happen in a work of Mozart and Beethoven is already to some extent audible in its opening, there is absolutely nothing about the theme of the Fugue in B-flat minor from the Well Tempered [Klavier], Book II that allows us to hear that it can be played in stretto at the ninth at the distance of one beat. Yet this quality of the theme, together with the even more complicated possibility of playing it in stretto with its own inversion in double counterpoint at the tenth, is essential to the shape of this fugue. All this is latent in the theme, but not audibly active when we hear it. [...] In [his] comprehension of these latent musical relationships, in his ability to draw from them all their power and significance, Bach was without equal in the history of music.

—Charles Rosen, from, Keyboard Music of Bach and Handel