Fugue

A fugue is a contrapuntal composition built on the systematic imitation of a single melodic subject across three to five voices. The exposition states the subject in the first voice (typically in the tonic), then the second voice enters with the answer (a transposed version in the dominant), then the third voice with the subject again in the tonic, and so on until all voices have entered. Episodes — passages of free counterpoint based on motivic fragments — alternate with further entries of the subject in various keys and stretti (overlapping entries). A fugue may stand as an independent piece or as the final section of a prelude-and-fugue pairing or a chorale-prelude. The form rewards extreme contrapuntal discipline; voice-leading rules from the species counterpoint tradition apply throughout.

Contrapuntal imitation as a procedure dates to the Renaissance ricercare and canzona, but the fugue as a worked-out independent form was perfected in the late Baroque, above all by J.S. Bach. His Well-Tempered Clavier (Book I, 1722; Book II, 1742) contains 48 prelude-and-fugue pairs spanning every major and minor key, and is the foundational study collection for any composer working contrapuntally. 'The Art of Fugue,' BWV 1080 (c. 1740-1750), is an unfinished cycle of fourteen fugues and four canons all derived from a single subject — a kind of treatise in pure form. After Bach, fugue became more often a section within larger works (the finale of Beethoven's Hammerklavier Sonata, Op. 106, or Brahms's Variations on a Theme by Handel, Op. 24) than a standalone form, though Shostakovich revived the standalone format with his 24 Preludes and Fugues, Op. 87 (1951).

Find the subject on its first appearance — usually unaccompanied — and then track it through the other voices. The subject may invert (turn upside down), augment (slow to twice its original length) or diminish (compress to half) in later sections, and a sharp listener catches these transformations even at speed. The end of a fugue often features a pedal point (a long held bass note over which other voices intensify), which sets up the final cadence.

Bach's Fugue in C minor from the Well-Tempered Clavier Book I, BWV 847 (1722), is a clean four-voice entry. For the standalone organ fugue, the Fugue in G minor 'Little,' BWV 578. Sviatoslav Richter's Well-Tempered Clavier and Glenn Gould's are the two most-discussed complete recordings.

Bach's unfinished final fugue from 'The Art of Fugue' breaks off mid-bar after the entry of a subject derived from the letters B-A-C-H (in German notation, B-flat, A, C, B-natural) — his own signature woven into the contrapuntal fabric. The piece stops with no closing cadence, and scholars still debate whether the missing section was completed and lost or never written.