Editing Tetrachord (section)

==Compositional forms==
The tetrachord, a fundamentally incomplete fragment, is the basis of two compositional forms constructed upon repetition of that fragment: the [[Lament bass|complaint]] and the litany.

The descending tetrachord from tonic to dominant, typically in minor (e.g. A–G–F–E in A minor), had been used since the Renaissance to denote a lamentation. Well-known cases include the ostinato bass of Dido's aria ''When I am laid in earth'' in [[Henry Purcell]]'s ''Dido and Aeneas'', the ''Crucifixus'' in [[Johann Sebastian Bach]]'s Mass in B minor, BWV 232, or the ''Qui tollis'' in [[Mozart]]'s Mass in C minor, KV 427, etc.<ref>Ellen Rosand, "The Descending Tetrachord: An Emblem of Lament", ''The Musical Quarterly'' 65, no.&nbsp;3 (1979): 346–59.</ref> This tetrachord, known as ''lamento'' ("complaint", "lamentation"), has been used until today. A variant form, the full chromatic descent (e.g. A–G{{Music|#}}–G–F{{Music|#}}–F–E in A minor), has been known as ''[[Chromatic fourth|Passus duriusculus]]'' in the Baroque ''Figurenlehre''.{{Full citation needed|date=January 2014}}<!--Author, year of publication, location, and publisher needed.-->

There exists a short, free musical form of the [[Romantic music|Romantic Era]], called ''complaint'' or ''complainte'' (Fr.) or [[Lament bass|lament]].<ref name="Dupre, Marcel 1937 p. 14">Marcel Dupré, ''Cours complet d'improvisation a l'orgue: Exercices preparées'', 2 vols., translated by John Fenstermaker. Paris: Alphonse Leduc, 1937): 1:14.</ref>  It is typically a set of harmonic [[Variation (music)|variations]] in [[Homophony|homophonic]] texture, wherein the bass descends through some tetrachord, possibly that of the previous paragraph, but usually one suggesting a [[Minor scale|minor mode]].  This tetrachord, treated as a very short [[ground bass]], is repeated again and again over the length of the composition.

Another musical form, of the same time period, is the ''litany'' or ''litanie'' (Fr.), or ''lytanie'' (OE spur).{{sfn|Dupré|1962|loc=2:110}} It is also a set of harmonic [[Variation (music)|variations]] in [[Homophony|homophonic]] texture, but in contrast to the lament, here the tetrachordal fragment – ascending or descending and possibly reordered – is set in the upper voice in the manner of a [[chorale prelude]].  Because of the extreme brevity of the theme and number of repetitions required, and free of the binding of [[chord progression]] to tetrachord in the lament, the breadth of the [[harmony (music)|harmonic excursion]] in litany is usually notable.