Baroque composers were still influenced by the ancient hexachordal system and conceptualized moving between the different hexachords to be a natural part of their musical vocabulary. Nowadays, we use terms such as tonicization and modulation to describe the alteration of accidentals.
Lets look at some of the voice leading patterns we have explored and see how this concept can be applied to them.
We start with the descending 7-6 sequence:
The ancient solmization of the bass here would start fa-mi-re-ut in the hard hexachord of C major. However, we can also think of this as the natural hexachord of G major and briefly use F# in the middle voice:
Or with the voices inverted:
This interprets the bass line B-A-G as a TC in G major (3-2-1).
Could we do the same thing with rising 5-6 sequence?
The first four bass notes Ut-Re-Mi-Fa are exactly 5-6-7-8 of a scale. So we can use the soft hexachord to cadence to F:
Perhaps surprisingly, the most useful for modulation is the 2-3 descending sequence.
If we look at the two part variant, we see it doesn’t require any accidentals to reach G as Ut:
If we want to emphasize G further as a cadential moment we can add D in the bass (to create a bass clausula).
What other notes would we add if the texture had three or more voices?
It seems pretty obvious that we would add either a C or a G to the first measure. Measure 2 would become a Clausula Altizans with F#-G (7-8) in an upper part and the rest of the progression will take on the form of a perfect authentic cadence in G major.
Here is the same progression with figures:
And in four parts:
