The exposition

The Contrapunctus I from the Art of the Fugue (Die Kunst der fuge BWV 1080) by J. S. Bach begins by presenting the subject in the alto:

The soprano answers with a tonal answer:

The tonal answer is in the key of A minor.

The counterpoint that goes with the answer has several interesting aspects:

• Notes in red are related to the subject as well as the motives a, b and c.
• Motive a is based on the first notes of the answer.
• Motive b is based on the last notes of the subject.
• Motive c is the inversion and augmentation of motive b.

The bass and tenor present voices 3 and 4:

• The subject played by the bass (measure 9) is accompanied by motive a in a kind of dialog between the soprano and alto voices. Motive b is also used.
• The answer is played by the tenor (measure 13) and the bass plays the same counterpoint used with the first answer (marked by a rectangle).
• A new motive d is played by the alto and the soprano. It is related with notes 4 to 6 of the subject.

The exposition ends in measure 17.