The Exposition

Bach's BWV 885 fugue from the second book of the WTC offers excellent examples of invertible counterpoint. The subject (S) of fugue BWV 885 is presented by the tenor:

In measure 5 the tonal answer (A) appears in the alto while the tenor plays the countersubject (CS):

This countersuject will have an important role in this fugue. Not only it will appear each time a subject or answer is presented, but it will also be used in episodes and offer numerous examples of inverted counterpoint at the 8th, 10th, 12th and the 13th with the subject.

The soprano presents the second subject (S) in measure 9 while the alto plays the countersubject (CS):

In measure 13 the bass presents the answer (A) while the countersubject inverted at the 8th appears in the soprano: