Which enharmonic to use when writing down a sequence of chords

Question

I've got a sequence of chords, denoted using solmization here:

S:  re  di  do  ti
A:  ti  TA  la  sol
B:  fa  mi  ri  re

I'd like to write down these chords in B flat major. I'm concerned with the second tone of the alto (the all-caps "TA"). In B flat major, it's either A flat or G sharp.

My question is: which one of the two enharmonic equivalents (A flat or G sharp) is more "correct", more idiomatic to write in this specific case? I. e., should I write

S:  C      | B               | B flat  | A
A:  A      | >>> A flat  <<< | G       | F
B:  E flat | D               | C sharp | C

or

S:  C      | B               | B flat  | A
A:  A      | >>> G sharp <<< | G       | F
B:  E flat | D               | C sharp | C

?

I know that the choice of enharmonic depends on the context of the notes; here's what I was able to come up with so far:

• This sequence of chords is descending, so maybe the A flat would be more appropriate;

• However, 'di' (B) naturally resolves to 're' (C), and as such, it might be regarded as the leading-tone of C. Hence, the note in question is enclosed between the major sixth formed by D and B, and since the chord is the fourth-sixth translation of the tritone G sharp–B-D, we could write G sharp as well.

So, I can't quite decide between the two. What gives?

Answer 1

Use flats. In fact, write the bass of the 3rd chord as D♭. You're not only running parallel second inversion diminished chords downwards, you're doing so in a key that already uses flats in the key signature. I'd even be tempted to write the soprano and bass of the second chord as C♭ and E♭♭ respectively, but leaving them be might be a little easier to read.

Answer 2

To add to Patrx2's answer, you will call the note Ab (for the key Bb). The reason why is because you're referring to the seventh scale degree when you label the pitch "ta" (we called it "te" but that's not the subject of the question :) ). Ti, Te, or Ta all refer to a pitch of the seventh scale degree. And so it must be a note that starts with the letter A (be it A, A#, Ab, etc.), which is also the seventh scale degree, for the key of Bb.

On the other hand, if the syllable was labeled "li" (i.e., raised "la"), or "la" or "le", you would refer to it as some form of the sixth scale degree (G), and in this case it would be G#. However, as Patrx2 mentioned, flats lead downward (and sharps lead upward), so "li" would have been awkward and functionally unconventional in terms of voice leading.

So go with Ab!