|Op 87 - No. 18 - F minor - Fugue|
Much of the ensuing density, complexity and ultimately ambiguity comes from the use of stretto. Nearly half of the subject entries occur in stretto with other entries, all within a single stretch of the fugue in a pattern of every increasing proximity. The first instance of stretto has two subject entries separated by two measures. After a brief episode, all four voices enter in stretto, this time, with each imitative entry separated by only one measure. Without break following the last of the four subject entries, three voices enter in stretto yet again, this time separated by only one beat, that is, half of a measure. As the proximity of stretto increases, it is harder and harder to follow any single subject entry: the opening motive of the subject commands your attention with each new entry causing you to loose your place in the old one. At first, it seems that perhaps Shostakovich is using only this motive, creating the drama of stretto with a series of partial, fragmentary and ultimately "false" subject entries. Remarkably, this is not the case: every subject entry runs to completion.
The final subject entry appears by itself without overlapping any additional subject entries in stretto. Indeed, the final texture is just the opposite: homophonic. The tenor part enters with a subject in G flat while the other three voices form unified chords sounding a cadence ending in F major. The chords persist while the final, lone voice finishes the subject "in the wrong key", reconnoiters, and returns with the ending of the subject again, this time in the key of F.