stretto fugue
A section of a fugue where subject entries overlap, with each voice beginning the subject before the previous voice has finished it, creating intensifying contrapuntal complexity.
In Depth
Stretto (Italian: "tight" or "compressed") is a fugal technique where entries of the subject pile on top of each other in increasingly rapid succession. In a normal fugal exposition, each voice states the complete subject before the next voice enters. In stretto, the second voice begins the subject before the first voice has finished, creating an overlapping, accumulating effect that builds excitement and contrapuntal density.
Bach was the supreme master of stretto, designing fugue subjects that could be combined with themselves at various time intervals and pitch transpositions. The final fugue of the Well-Tempered Clavier Book I (BWV 869) and the "Great" Fugue in G minor (BWV 542) contain magnificent stretto passages. Stretto is typically deployed as a climactic device, reserved for the later sections of a fugue to create a sense of culmination. The ability to write a subject that works in stretto at multiple intervals is one of the highest tests of contrapuntal craft.
Bach designed his fugue subjects like mathematical puzzles — the best ones work in stretto at multiple intervals, in inversion, and even in retrograde, though he hid this extraordinary craftsmanship behind effortlessly beautiful music.