Does music theory provide a language for directly expressing voice leading? Roman numeral analysis (RNA) encapsulates voice-leading expectations, but these are built in by implication (indirectly) to what is a harmonic (vertical) language. Is there a more directly melodic (horizontal) language?
The origin of the question
In Bach's setting of the chorale "Ach Gott, vom Himmel sieh' darein" (BWV 2) (IMSLP: chorale #3) (YouTube), the final phrase is harmonically complex, but voice-leadingly simple(r). A harmonic (Roman numeral) analysis doesn't convincingly capture (IMO) what's actually happening compositionally.
Does "music theory" provide an analytical language for voice leading outside of the voice-leading expectations built into RNA? That is, is there a way to express voice leading directly?
If yes, a demonstration of how that language would be applied in this situation would be very helpful. Here is the score of the phrase in question. (Note: The preceding phrase cadences in A minor.)
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