String Quartets, Op. 51, Numbers 1 and 2, Op. 67

String Quartet No. 1 in C minor is remarkable for its organic unity and for the harmonically sophisticated, "orchestrally inclined" outer movements that bracket its more intimate inner movements. Structurally and thematically, the first movement shows the influence of Schubert's Quartettsatz, D. 703, also in C minor. The String Quartet No. 2 in A minor, also highly unified thematically, is comparatively lyrical, although culminating in a dramatic and propulsive finale whose tension "derives...from a metrical conflict between theme and accompaniment." Like Brahms's Piano Quartet No. 1 and Violin Concerto, the A minor quartet has a final movement modeled on a Hungarian folk dance, in this case a czárdás. With all the movements in A minor or A major, the String Quartet No. 2 is therefore homotonal. - Wikipedia.

To round the threesome out, Brahms composed a bright and sunny work in B flat major that happens also to be one of the most flawlessly-crafted items in the repertoire. The first of the quartet's four movements is a Vivace in 6/8 time. Brahms seems to be having great fun throwing accents and sforzandos into the "wrong" parts of the measure throughout the spiccato first theme. The second theme is similarly fun-loving -- it moves into 2/4 time leaps around on a little dactylic rhythm (long/short-short) and sounds, at least until the legato second strain of the theme arrives, uncannily like a famous children's folk song. An Andante in F major serves as the slow movement; it has in the middle of it two measures of 5/4 time -- an unusual thing for Brahms. An Agitato (Allegretto non troppo) fills the scherzo position and is written in true da capo form. The glory of Op. 67, many feel, is the extraordinary final theme and variations movement (Poco Allegretto), at the end of which the theme of the first movement makes an encore appearance. - Blair Johnston at allmusic.com