Haydn was an early cultivator of the string quartet. His first works for the combination of instruments (two violins, viola, and cello) were lighter in tone, an intimate version of the serenades and divertimentos called on to accompany the events of life at the princely court where Haydn worked. The set of six quartets, Op. 20, finds the composer delving deeper, intensifying the music's emotional expression and adding layers of complexity not found in his previous quartets. (Beethoven made a copy of one of the Op. 20 quartets during his student days in Vienna.) This is the moment when the string quartet leaves the traces of its lighter origins behind and becomes a full-fledged genre of serious instrumental music to rank alongside the classical symphony. As the great musicologist Donald Tovey put it, "With Op. 20 the historical development of Haydn's quartets reaches its goal; and further progress is not progress in any historical sense, but simply the difference between one masterpiece and the next."

The autograph manuscripts for the six quartets are dated 1772. They were published as "Opus XX" by Chevardière in Paris in 1774 and again by Hummel in Amsterdam five years later with an image of the sun on the title page, which explains the nickname carried by the set - the "Sun" quartets - and in the order still used today, with the F-minor quartet as No. 5.

The opening movement of Op. 20, No. 5, is a fascinating study in how harmonic shifts transform thematic material. The rather desolate opening theme, for example, gains tremendously in warmth and extroversion when rendered in the major mode at the beginning of the movement's development. We also encounter passages of virtuosic writing for the first violin, which would have been played by Luigi Tomasini, the gifted concertmaster of the court orchestra directed by Haydn. The austere minuet, with its trio of folk-like simplicity, precedes the A-flat-major slow movement, which unfolds in the manner of an operatic aria with the first violin taking the "sung" part. The finale, a densely argued two-part fugue, finds Haydn looking back to the Baroque, the heyday of the fugue, to underscore his vision of the string quartet as a place for profound musical expression.

- John Mangum is the Los Angeles Philharmonic Association's Program Designer/Annotator.