The second movement is in binary form but organized like an invention or fugue. The first two measures play the role of an exposition, where the subject or theme appears for the first time. Episodes follow the exposition. Often, these episodes are harmonic marches that will take us to new keys where Bach will introduce the subject or theme again.
In this movement, the cellos always play in unison, doubled by the violone and continuo. Click on the sections for a detailed analysis.
Part B begins in D major. The cellos and continuo present the subject and extend it (dashed frame).
We move to E minor in measure 14. The subject passes to the violas. Bach transforms the first two notes into G and F# (instead of E - D#) to have the third of the E minor chord in one of the voices.
Notice how the instruments exchange thematic material: violins to cellos, violas to violins, and cellos to violas.
We reach the key of E minor in measures 15 and 16.
Once in E minor, the instruments present the subject like the first measures of the A part:
A march similar to the previous ones takes us to B minor, and the viola I presents the subject with its first notes transformed in measure 20:
The subject presentations continue. In measure 22, third beat, the march of fourths and fifths begins:
The march always led us to modulate an ascending fifth. This march takes us to F# major, but the F# is used as the dominant of B minor. It begins a passage similar to the last measures of section A that will affirm the key of B minor:
The semiquaver arpeggios increase the intensity of the passage:
The key of B minor is affirmed on the third beat of measure 28: