The Third Subject

The third subject is based on the main subject of the Art of the Fugue. Let's start with the original subject:

Transform it by inversion:

The subject is a rhythmical variation of the inversion:

The alto voice presents the subject in measure 94 followed by the bass in measure 99 and the soprano in measure 105. The bass uses a kind of tonal answer. It begins on D but the key is A minor. The third appearance on the soprano is clearly the subject transported to the A minor key:

Another episode follows (measures 110 to 124). In measure 125 (alto) and 131 (bass) the first subject reappears followed by another episode (measures 135 to 146) that precedes the first simultaneous appearance of the three subjects in measure 147.