Bass Clausula
The typical bass motion at a full close: usually a fifth down or a fourth up, from dominant to tonic.
What it means
The bass clausula is the standard bass movement that harmonically completes a full close (clausula finalis). The bass falls a fifth, or equivalently leaps a fourth upward, moving from the dominant to the tonic.
The term comes from older counterpoint theory, which described each voice of a cadence with its own clausula: alongside the bass clausula, this theory also recognizes a discant clausula for the upper voice.
Musical use
The bass clausula occurs in virtually every cadence of tonal music, from Renaissance vocal polyphony to functional harmony. It supplies the harmonic grounding while the other voices may unfold different melodic closing formulas.
It should be distinguished from the deceptive cadence, where the expected motion to the tonic is replaced by another scale degree, and from the half cadence, which ends on the dominant and precisely does not complete the bass clausula.
Performance practice
When realizing figured bass or listening to classical cadences, notice how surely the falling fifth in the bass marks the close. In many pieces you can hear the approaching cadence in the bass before the upper voices reach their resolution.