Descending tetrachord

Descending tetrachord in a minor: scale degree 8-♭scale degree 7-♭scale degree 6- scale degree 5 (a-g-f-e) Playⓘ.
The Phrygian progression creates a descending tetrachord bassline: scale degree 8-♭scale degree 7-♭scale degree 6- scale degree 5.
Phrygian half cadence: i-v6-iv6-V in c minor (bassline: c -b♭-a♭-g) Playⓘ.

In music theory, the descending tetrachord is a series of four notes from a scale, or tetrachord, arranged in order from highest to lowest, or descending order. For example, scale degree 8-♭scale degree 7-♭scale degree 6- scale degree 5, as created by the Andalusian cadence. The descending tetrachord may fill a perfect fourth or a chromatic fourth.