By contrast to sectional variation form, in which a self-contained theme (almost always in binary form) is repeatedly presented in varied form, continuous variation form is created by repeated variation of a pattern that is not self-contained. Often the pattern is a bass progression, with new melodic materials freely added over the bass. Continuous variation form was popular in the Baroque period, but it is still popular today -- every Blues performance and Jazz improvisation over Blues changes is a kind of continuous variation form.
Henry Purcell, "Dido's Lament" from Dido and Aeneas
Preceded by the recitative "Thy Hand, Belinda," this aria consists of eleven variations on a five-measure repeated bass pattern. Like most such patterns, it begins on the tonic and ends on the dominant.
What sectional form we have studied do the key changes in m. 133 and m. 209 divide the movement into?
Here the tune's chorus (mm. 19-42) comprises two variations on the standard 12-bar Blues progression. Be sure to listen to Louis Armstrong's historical improvisation on this standard.