His music is highly polyphonic, and modern in its instrumental treatment throughout.
As music becomes more polyphonic the inner parts of the orchestra become more and more emancipated.
This is of constant occurrence in classical pianoforte music, in which thick chords are subjected to polyphonic laws only in their top and bottom notes, while the inner notes make a solid mass of sound in which numerous consecutive fifths and octaves are not only harmless but essential to the balance of tone.
Bach's conception of the function of an instrument is that it holds a regular part in a polyphonic scheme; and his blending of tones is like the blending of colours in a purely decorative design.
Far greater polyphonic detail of another kind is no doubt possible, but it requires far longer time for its expression.
They are an extension of the principle on which gongs and cymbals and all instruments without notes of determinate pitch are employed in otherwise polyphonic music.
In the famous dedicatory letter of his Alceste he mentions among other conceptions on which his reform of opera was to be based, that the co-operation of the instruments ought to be regulated in proportion to the interest and the passion, a doctrine of which the true significance lies in its connexion with other conditions of opera which are incompatible with the polyphonic treatment of instruments as threads in a decorative scheme.
To write an account of symphonic instrumentation in any detail would be like attempting a history of emotional expression; and all that we can do here is to point out that the problem which was, so to speak, shelved by the polyphonic device of the continuo, was for a long time solved only by methods which, in any hands but those of the greatest masters, were very inartistic conventions.