In a letter to André Gertier, Bartók described the first movement as being in sonata form, the second as "a kind of rondo" and the third as "difficult to define" but possibly a sort of ternary form. Zoltán Kodály, who thought of the three movements of this quartet as "life episodes," heard "peaceful life" in the first movement, and for all its roiling emotions, the movement does indeed leave an impression of tranquility at the end.
The brooding, intense last movement (Kodály heard it as "suffering") is particularly funereal because it is as immobile as the second movement is animated. Long stretches are rhythmically static, and the parts that do move are often interrupted by silence.[1]
Bartók Quartet No. 2, lecture by Roger Parker, followed by a performance by the Badke Quartet, Gresham College, 4 December 2007 (available for download as MP3 or MP4, as well as a text document)