Fugue

A fugue is a work or passage organized around systematic imitation of a principal melodic idea, the subject, in multiple contrapuntal lines. Each line, or voice, has some independence while combining with the others. A voice need not be sung by a separate performer: keyboard music can make several lines audible through one instrument. The word also describes a compositional technique used within a larger work, not just a self-contained piece. A fugue is more flexible than a strict canon, in which successive voices repeat the same melody according to a fixed rule.

In a typical exposition, one voice presents the subject; another then enters with an answer, usually a transposition toward the dominant, while the first voice continues. The remaining voices enter in turn, though the number and order of voices can vary. A real answer closely transposes the subject, whereas a tonal answer adjusts some intervals to preserve the musical key. A countersubject is a recurring line that accompanies the subject or answer, but not every fugue has one. After the exposition, composers may alternate further subject entries with episodes, which develop fragments or other material rather than state the entire subject. The length, number of voices and later arrangement are determined by the composer, so these features describe common practice rather than an unvarying form.

The term fuga was applied to canonic music by the 14th century, but the word's meaning and use changed over time. Closely imitative passages in late-16th-century canzonas and ricercares are among the predecessors of the more developed fugue. In the 17th and early 18th centuries, fugue became an important compositional genre, especially in keyboard and vocal music. Johann Sebastian Bach's The Well-Tempered Clavier, published in two books in 1722 and 1744, paired a prelude and fugue in each of 24 major and minor keys per book. George Frideric Handel also wrote prominent choral and instrumental fugues. Although fugue was no longer central to mainstream composition by the mid-18th century, composers continued to study and use it. Ludwig van Beethoven and later composers renewed and adapted the technique in large-scale vocal and instrumental works.

Fugues can be written for voices or instruments, for solo performers or ensembles, and in sacred or secular settings. The number of contrapuntal voices is not the same as the number of musicians: one keyboard player, for example, can perform a multi-voice fugue. Bach's Well-Tempered Clavier is a widely studied example of the genre, while fugues by Handel and Beethoven show how the technique was used in choral, orchestral and chamber music as well as keyboard works. In analysis, listeners and musicians often follow the subject and answer as they pass between voices, then notice how episodes and later entries transform the original idea.