in music, a melodic or chordal figure repeated at a new pitch level (that is, transposed), thus unifying and developing musical material. The word sequence has two principal uses: the medieval (Middle Ages) sequence in the liturgy of the Latin mass and the harmonic sequence in tonal music.

In medieval music and literature, the sequence was a Latin text associated with a specific chant melody, to be sung at mass between the Alleluia (hallelujah) and the reading of the Gospel. It developed about the 9th century from the trope (addition of music, text, or both) to the jubilus, the florid ending of the last syllable of the Alleluia. The melodic tropes were normally broken into phrases that were repeated in performance (as aa, bb, cc,…) by alternating choirs. Texts set to these and to Alleluia melodies were originally prose and thus were referred to by the medieval Latin name prosa.

By the 11th century the sequence had developed a common poetic form that reflected the musical structure: typically, introductory and closing lines enclosed a series of rhymed, metrical couplets of varying lengths (x aa bb cc…y). Each syllable was set to a single note of music. Eventually, texts were set to newly composed melodies, and the lengths of the couplets were equalized. Sequences became highly popular throughout Europe, and thousands of examples of them survive that are appropriate to different liturgical feasts. In the 16th century the Council of Trent (Trent, Council of) abolished all but four sequences from the liturgy: Victimae paschali laudes (“Praise the Paschal Victim”), Veni Sancte Spiritus (“Come Holy Spirit”), Lauda Sion (“Praise Zion”), and Dies irae (“Day of Wrath”). The Stabat mater dolorosa (“The Sorrowful Mother Was Standing”) was reinstated in 1727.

Secular musical forms influenced by the sequence include the estampie (a dance) and the lai (a song genre of the trouvères (trouvère), medieval French poet-composers).

Though easily abused if applied mechanically, the harmonic sequence has been widely employed by all composers of tonal music, that is, those active from roughly 1700 to about 1900. Very long sequences appear in concerti of the Baroque era, especially in the works of George Frideric Handel (Handel, George Frideric) and Antonio Vivaldi (Vivaldi, Antonio). Often the sequence is used for modulation in the development section of a sonata form, as in the first movement of Beethoven (Beethoven, Ludwig van)'s Symphony No. 1 in C Major (1800). A remarkable extended series of modulating sequences is a feature of the development section of Frédéric Chopin (Chopin, Frédéric)'s Piano Concerto No. 1 in E Minor (1830).