The Lament Bass is a Ground Bass or Passacaglia, built on a descending perfect fourth from the tonic to the dominant.
The Diatonic version of the Lament Bass uses descending 8-7-6-5 in natural minor.
Early harmonizations of this progression commonly used 5/3 on the first and last note (with #), and 6/3 on the passing bass notes. If played only once, this is also known as a Phrygian cadence or a “mi cadence.”
Phrygian Cadence
If considered in the Phrygian mode (E is the finalis), the top and bottom voices create a TC/DC pair. The syllables are different and the half steps are different, but the idea is the same: TC ends with a half step (F-E) and the DC with a whole step (D-E).
A compound mi cadence will look like this:
Rule of the Octave
Another common possibility is to use the descending rule of the octave in minor – note that this will result in a french chord on scale degree 6. Below is the example from Fenaroli’s manual on the Rule of the Octave.
Chromatic Lamento Bass
This includes a chromatic motion from 1 down to 5. We can still keep 5/3 on the first and last bass note, and 6/3 in between.
Chromatic Lamento with Alto Clausula
Another option is to use 5/3 and 6/3 for the first two bass notes followed by a +4/2 figure on the third bass note. This then resolves as an alto clausula to bass note five.
With Roman Numeral Analysis
The fifth figure can stay 6/3, or become +6/4/3 like in the rule of the octave. However, a common variant uses a +6/5/3 – or a German 6 chord instead.
