J.S. Bach Analysis - BWV889 - WTC II - XX Fugue in A minor

It is not strange at all; on the contrary: if you compare the other three-voice Fugues from the WTC, you will see that this one (S – R – div – S – div ...) is the most common situation.

The exposition of the Fugue in D minor from WTC I follows the scheme S – R – div – S – R, but the last entry is not on the D but on the t, with a completely irregular modulation.

Even the Fugue in A Major from WTC II does not seem to properly follow the S – R – div – S – R scheme, because at m. 6 there is a half-measure connecting divertimento that does not appear at m. 2.

The only true exception I have found is the Fugue in Bb Major from WTC I, where the scheme is indeed S – R – div – S – R (with T-D-T-D).

At measure 9 you find a variant of the subject (the head changes) which uses as a bass for part of the divertimento and at measure 13 proposes the "true" answer in the key of the dominant.

RedScharlach wrote:

The only true exception I have found is the Fugue in B-flat minor from WTK I, where the pattern is actually S – R – div – S – R (with T-D-T-D).

For example, the D minor fugue from the second book has the 4 entries in sequence. The B natural in the bass is interesting