ii65 is a good example. According to my textbooks, the dissonant ^1 in this chord requires a more strict preparation than the ^4 of the V7 chord in common practice harmony which many times is not prepared at all. With the ii7 and its inversions the preparation is supposed to be more important via suspension or passing tone. The thing I dont get is that once you invert this chord to be ii65, the dissonant ^1 becomes consonant with the bass as a parfect 5th so why should it be prepared?
3 Answers
The ^1 may be consonant with the ^4 bass, but it is dissonant with ^2, usually in the melody. Remember that voice leading rules developed from counterpoint rules, and harmony also developed from counterpoint. We tend to think of voice leading as a constraint that restricts what you can do with a given harmony, but that's somewhat backward.
The ii6/5-V-I cadence is another way of harmonizing a descending ^3 ^2 ^1 cadence with a ^1 ^7 suspension (in, e.g., the alto). It could also be harmonized as V with a 4-3 suspension; the difference is in the bass (and the other inner voice). But this melodic cadence is far more ancient than harmony
Add to this that the seventh of the seventh chord may arise not as a prepared suspension but as a descending passing tone. In the V-V7-I case, that's ^5 ^4 ^3, and in the other case, ^2 ^1 ^7. But in the second case, there's a good chance that ^2 isn't doubled in the ii6 chord, so when the voice with that pitch moves to ^1, we don't have a ii6/5 chord but a IV chord.
In short, there are both contrapuntal and historical grounds for treating the ii6/5 chord distinctly from the V7 chord.
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So then why not prepare the ^2?– user35708May 11, 2022 at 13:26
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@armani what chord precedes the ii6/5? Normally some inversion of I, which has a ^1 in it but not a ^2.– phoogMay 11, 2022 at 13:29
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ahh ok, that makes sense– user35708May 11, 2022 at 13:32
In the context of traditional harmony textbooks, when considering whether or not a note is dissonant we must take into account all the notes in its harmony. The fact that the ^1 in a ii65 is consonant in relation to the bass does not change the fact that it is dissonant in relation to ^2. ^1 will always be a dissonance in the tetrad over the ii, no matter what inversion it happens to be in.
I see no reason why any of these variants of II-V-I require preparation of the melody note more than any other. If your book thinks otherwise, it's down to the author to say why.
I see I didn't actually include a ii6/5. Sorry! Add a D in the tenor of the third one.
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