The last movement of the G major quartet is written in strict form, and highly interesting by reason of the elegance of its counterpoint; the finale of the A major quartet is freer and easier, but nevertheless polyphonic in treatment.[20] The D minor quartet concludes with variations, the original and long-drawn theme having the rhythmical and sharply accented harmonic form of the siciliana. It is in imitation of a national song, and is sometimes like a slow gigue, sometimes like a pastorale. The rhythm of the 6-8 time is somewhat peculiar, in that the first of three quavers is dotted throughout; the tone is soft and tender. There is a very similar siciliana in Gluck's ballet "Don Juan" (No. 2), showing how marked the typical character is.[21] The variations, which are as charming from their grace and delicacy of form as from their singular mixture of melancholy and mirth, bring this wonderful quartet to a close in a very original manner.
The middle movement of the A major quartet is also in variations--more earnest and careful on the whole--the precursor of the variations in Haydn's "Kaiser" and Beethoven's A major quartets. These quartet variations far surpass the pianoforte variations in character and workmanship; they consist not merely of a graceful play of passages, but of a characteristic development of new motifs springing from the theme.
The success of the quartets, on which Mozart put forth all his best powers, was scarcely sufficient to encourage him to make further attempts in the same direction; not until August, 1786, do we find him again occupied with a quartet (D major, 499 K.), in which may be traced an attempt to
meet the taste of the public without sacrificing the dignity of the quartet style. It is not inferior to the others in any essential point. The technical work is careful and interesting, the design broad--in many respects freer than formerly--the tone cheerful and forcible throughout, with the sentimental element in the background, as compared with the first quartets. The last movement approaches nearest to Haydn's humorous turn of thought, following his manner also in the contrapuntal elaboration of a lightly suggested motif into a running stream of merry humour. Nevertheless, this quartet remained without any immediate successor; it would appear that it met with no very general approval on its first appearance. "A short serenade, consisting of an allegro, romance, minuet and trio, and finale" in G major, composed August 10, 1787 (525 K.), does not belong to quartet music proper. The direction for violoncello, contrabasso, points to a fuller setting, which is confirmed by the whole arrangement, especially in the treatment of the middle parts. It is an easy, precisely worked-out occasional piece.