Sequence
a series of things following in a certain order or succession; specifically, a set of cards immediately following each other in the same suit, as an ace, two, three and four. In music, the recurrence of a harmonic progression or melodic figure at a different pitch or in a different key to that in which it was first given. A tonal or diatonic sequence is when no modulation takes place. A chromatic or real sequence takes place when the recurrence of a phrase at an exact interval causes a change of key.
In the Roman ritual, a rhythm sometimes sung between the Epistle and the Gospel. At first it was merely a prolongation of the last note of the Alleluia, but afterward appropriate words were substituted. When the Roman Missal was revised in the 16th century, only four of the existing sequences were retained: Victinæ Paschali, for Easter; Veni, Sancte Spiritus, for Pentecost; Lauda, Sion, for Corpus Christi; and the Dies Iræ, for Masses of the Dead. The Stabat Mater, for the Feast of the Seven Dolors, is of later date . per