Lament bass

In music, the lament bass is a ground bass, built from a descending perfect fourth from tonic to dominant, with each step harmonized.

[1] The diatonic version is the upper tetrachord from the natural minor scale,[2] known as the Phrygian tetrachord, while the chromatic version, the chromatic fourth, has all semitones filled in.

[3] However, "A common misperception exists that the 'lament bass' of Venetian opera became so prevalent that it immediately swept away all other possible affective associations with this bass pattern...To cite but one example, Peter Holman, writing about Henry Purcell, once characterized the minor tetrachord as 'the descending ground that was associated with love in seventeenth-century opera'.

[9] It is typically a set of harmonic variations in homophonic texture, wherein the bass descends through some tetrachord, possibly that of the previous paragraph, but usually one suggesting a minor mode.

This tetrachord, treated as a very short ground bass, is repeated again and again over the length of the composition.