Ph. Eman. Bach declared that the chief and best quality of music was melody,[29] and this principle once recognised, the laws of song were adopted by instrumental music, although with many modifications, to suit the different characters of the instruments and the necessities of thematic elaboration. The chief improvement was the spirited development of one or more subjects to replace the tedious middle movement of the aria. The artistic development of the separate elements, according to their true significance, introduced both contrast and climax; unity was assured, since nothing foreign either to the form or the substance was admitted; while the repetition of the first part, like a dialectic exposition of an argument, provided a clear and satisfying conclusion. This working-out part did not always receive its due share of honour, and was often treated as a form of harmonic transition; but it asserts itself more and more as the proper nucleus of the whole movement, and has an important reaction on the formation and phrasing of the first part. This becomes, as it were, the foundation prepared for the future development which first displays the whole extent of the conception. The coda was usually confined to a lengthened development of the closing phrase, and gathered to a point in pregnant brevity the most essential elements of the movement. It had its counterpart in the cadenza of the aria. After what manner great vocalists constructed their cadenzas we are unfortunately ignorant, but instrumental cadenzas reproduced the principal subjects of the movement, just as was the case in the coda. Beethoven, who brought the coda to perfection, has himself worked out the cadenzas in the Concerto in E flat major; the cadenza in the first part is identical in mechanism with the coda of one of his great symphonies. The original middle movement has preserved a slower {INSTRUMENTAL MUSIC.} (294)