If the language of music is merely the utterance of a melodic line, a simple sequence of musical notes, it can justly be accused of poverty. The addition of a Bass puts it upon a harmonic foundation and clarifies it, but defines rather than gives it added richness. A melody so accompanied—even though all the notes are not those of the true Bass—or treated with simple embellishments in the upper parts, or with simple chords, used to be called “homophony.” But it is a very different thing when two melodies are so interwoven that they converse together like two persons upon a footing of pleasant equality. In the first case the accompaniment is subordinate, and serves merely to support the first or principal part. In the second case the two parts are not similarly related. New melodic combinations spring from their interweaving, out of which new forms of musical expression emerge. If more parts are interwoven in the same free and independent manner, the apparatus of language is correspondingly enlarged, and becomes practically inexhaustible if, in addition, varieties of form and rhythm are introduced. Hence harmony becomes no longer a mere accompaniment of melody, but rather a potent agency for augmenting the richness and expressiveness of musical conversation. To serve that end a simple accompaniment will not suffice. True harmony is the interweaving of several melodies, which emerge now in the upper, now in the middle, and now in the lower parts. From about the year 1720, when he was thirty-five, until his death in 1750, Bach’s harmony consists in this melodic interweaving of independent melodies, so perfect in their union that each part seems to constitute the true melody. Herein Bach excels all the composers in the world.(143) At least, I have found no one to equal him in music known to me. Even in his four-part writing we can, not infrequently, leave out the upper and lower parts and still find the middle parts melodious and agreeable. But in harmony of this kind each part must be highly plastic; otherwise it cannot play its role as an actual melody and at the same time combine with the other parts. To produce it Bach followed a course of his own, upon which the textbooks of his day were silent, but which his genius suggested to him. Its originality consists in the freedom of his part writing, in which he transgresses, seemingly, at any rate, rules long established and to his contemporaries almost sacred. Bach, however, realised their object, which was simply to facilitate the flow of pure melody on a sound harmonic basis, in other words, successive and coexistent euphony, and he succeeded with singular success though by unfamiliar means. Let me explain my meaning more closely.