Fugue is a contrapuntal composition in which a theme is introduced and imitated across multiple independent voices.
A fugue opens with a single melodic subject stated alone, then answered by a second voice at a different pitch while the first continues with new counterpoint, then a third voice, and so on, until all the intended voices are in play, weaving the same thematic material through overlapping, independent lines. Unlike a strict form with fixed proportions, a fugue is better understood as a discipline or a game with rules — invertible counterpoint, stretto (overlapping entries of the subject), augmentation and diminution of the theme — that a composer plays against their own material. Johann Sebastian Bach is the form's unmatched master; his Well-Tempered Clavier and The Art of Fugue remain the benchmark against which every subsequent fugue, including those by Mozart, Beethoven, and Shostakovich, is measured. Because a fugue demands that a composer keep multiple independent lines simultaneously coherent and harmonically sound, it has long served as both a serious compositional exercise and a display of pure craft.