I would say that it's based on spelling which in this case indicates the function. Spelling is sometimes meaningful. Otherwise a German 6th is a dominant 7th, yes? Or maybe it is. Just not in this case. Context is everything.billygard wrote:
...unless it can be stated that the designation as a Tristan chord is based on spelling and not on voicing.
I will also say that while usually the explosion out to the octave was what's done in certain period practice, that the function is the most important thing in harmonic practice, that names should follow that. A "German 6th" F A C D# can go to E G# D and fulfill the function just the same. Hence my conflating it at some level with flat 5 substitution of dominant principle, and my word superdominant.
F A Cb Eb to E G# Bb D; I don't see that this is different than F A C D# to E G# [D] E, in function.
SO. What things are called is not the primary consideration. It seems to me 'it's the voice leading' follows, to some extent, 'it's a German sixth'.
F A B D# to F Ab B D... why wouldn't it be a french sixth there? is that an important question?