# sharp ii dim 7th: How to use?

Still here and working on part-writing. I have used a sharp ii dim7th chord, straight after iihalfdim7- leading to V. Is this actually the right place to put it in terms of chord sequence/harmonic progression? Obviously, as we are in minor, the ii chord is also dissonant, so the progression has to be treated very carefully.

I have voiced the two chords as follows. The key is E minor:

Potential issues:

1.As you can see, in the ii half dim7, I have an augmented 4th between the tenors and alto. This dissonance does not resolve in the next chord, and instead becomes another augmented 4th interval , just half a step up (C-Fsharp, Csharp-F double sharp). Is this acceptable/unavoidable?

1. I have leapt into a dissonance from A to F sharp in the tenor (F sharp being the augmented 4th of the dissonance). Is this also unavoidable? (perhaps a remedy here is to double the E [5th] of the previous chord, allowing a move by step into the dissonance? although this would be unorthodox doubling).

Thanks

Ed

• #ii in key Em is a simple G note - which means it's diatonic, so why use Fx?
– Tim
Commented Mar 27, 2021 at 14:37
• @Tim ii in Em is F#, so #ii is Fx. G is iii in Em. The larger problem is that in standard theory there's no such thing as a #ii chord. It would be some kind of applied or common-tone chord. The progression here doesn't make harmonic sense -- at least not without additional context. Commented Mar 27, 2021 at 15:52
• I agree. Knowing where the progression would/should go (and where it's coming from) would also be much more useful. Commented Mar 27, 2021 at 15:55
• Maybe more to the point - why does OP want/need #ii?
– Tim
Commented Mar 27, 2021 at 16:11
• @Tim, I'm guessing it's homework. :D Commented Mar 27, 2021 at 21:46

♯ii°7 is really only used for one of two reasons, and in both cases it will be labeled differently:

1. As a vii°7/iii to tonicize iii. Notice that this really only works in major keys, because in minor the root of ♯ii is enharmonically equivalent to the root of III.

2. As a common-tone diminished seventh (often labeled CT°7) expanding tonic.

Since you're in minor, the second option is really the only viable use of this chord, in which case you will typically go from i to this "♯ii°7" back to i. And since the purpose of the CT°7 is often to keep the common tone in the same voice, this "♯ii°7" will typically be in third inversion so that the bass E stays constant throughout.

For more on the common-tone diminished seventh, see the first half of this answer.

• Well, in minor, it wouldn't be enharmonically equivalent to the root of the target chord as long as the Fxdim7 chord then tonicizes some kind of G# chord instead of G. Pretty unlikely, of course. Commented Mar 28, 2021 at 2:12
• thanks for such a great answer Richard. I remember reading somewhere that sharp ii dim 7 can be used as a leading note dim 7th to V. This is actually how i was planning on using it here. (sharp ii dim 7-V). Do you have any knowledge of this function? Commented Mar 28, 2021 at 17:00
• @EdB123 Oh, interesting. In this case, that chord is best spelled with the raised fourth scale degree as root (a type of ♯iv°7 as opposed to ♯ii°7). This is enharmonic to ♯ii°7, but it's important to spell it with ♯iv as the root to show its function as a leading-tone chord resolving to V. That definitely happens, but I would say it comes after IV far more often than after ii. Commented Mar 28, 2021 at 17:06

You've discovered one of the tricks that Romantic piano music is based on-- throw layers and layers of dim7 chords one after the other, especially during your flashy crashy-bangy solo sections, and you'll get a dramatic sound that can end up on any key you want.

A fundamental rule in music is that raised tones rise. An augmented F wants to resolve a half-step up: to G#. I'd recommend g# minor, since it's going to be pretty easy to get to B7 and back to e.

One comment as a music teacher: write more NEATLY. Get a thick mechanical pencil (0.5mm is good) with a soft lead. And frame your page properly, because not doing so shows disrespect to the people whom you would like help from.

• This comment sets a pretty high bar, so maybe it should not end with a preposition. Commented Mar 27, 2021 at 23:04
• You think that was the kind of comment up with which the OP should not put? :D Commented Mar 27, 2021 at 23:06
• Qui docet discit? Commented Mar 27, 2021 at 23:23
• That's my main reason for being here. There are quite a lot of smart cookies, here! Commented Mar 27, 2021 at 23:53