Linear progression, Zug. A linear progression is a stepwise progression of a third or greater connecting structural notes of one or more harmonies. The fundamental line is a linear progression at the background level. Where two or more voices exhibit parallel linear progressions (in thirds or sixths), the linear progression that relates most directly to the underlying harmonic context, or to the fundamental line, is considered the leader.
The example, mm. 83-86 of the fugue, illustrates several linear progressions. The uppermost slur indicates a descending octave from f in m. 83 to f in m. 87 (not shown). The next series of slurs indicate fourth progressions that expand the motion f-c of mm. 83-86, which itself is a descending fourth-progression. More descending fourth-progressions are also found in the lower voice.