String Quartet in D major, Op.50, No.6 (Hob.III:49) (“Frog”)

If any instrument in the classical string-quartet democracy was allowed to be more equal than the others it was the first violin. So a conscientious composer writing string quartets for the cello-playing Friedrich Wilhelm II of Prussia, like Haydn in 1787 or Mozart two or three years later, had a problem. Haydn’s solution, unlike Mozart’s, was ostensibly to ignore the issue while discreetly giving the royal cello interesting things to do. Much the most important aspect of the first movement of his so-called “Frog” Quartet in D major, the last in the “Prussian” set, is the off-tonic entry of the first violin in the opening bar. The motif the violin has to itself at that point - a dotted minim followed by four descending semiquavers - is to reappear literally dozen of times either in its original form or in a shorter variant. It is the cello, however, that seems to motivate the early (if brief) change to D minor and it recalls that moment not only in the recapitulation but at two harmonically significant points in the development.

Where Haydn comes nearest to Mozart’s solution of the cello problem is in the slow movement. A siciliano beginning in D minor and ending opulently in D major, the Poco adagio is remarkable for its elaborately decorative texture, giving the cello several virtuoso opportunities but, crucially, treating the second violin and viola scarcely less generously while still preserving the supremacy of the first violin. The interest of the Menuetto, on the other hand, is not so much textural as rhythmic with its syncopations, diminutions and, in the unusually extended Trio section, metrical contradictions and sudden silences.

Instrumental colour is what the Finale is all about, or nearly all about. The main theme, which is introduced by the first violin in the opening bars, is characterised by the allegedly frog-like sound of its bariolage articulation, the same note alternating between two adjacent strings (usually one open and one stopped). Not just an entertaining device, it is eventually taken up by every instrument, the cello last of all, and worked into the very fabric of the construction. The second subject is much less prominent but, by recalling the shape of the main theme of the first movement, it performs a useful unifying function before the work quietly croaks its last.