#1
Out of boredom I took another look at the II-V Jazz lines video by Andrew Wasson that's been on the homepage for some time now. As usual for him it was a good informative video but I noticed that one of his examples in D minor went Edim7-A7-Dm7. He went on to say that a m7b5 could also be used in place of the dim7.

My question is how/why does the dim7 work there? I know that for standard seventh chord harmonization of the natural minor scale the m7b5 is the harmonically "correct" choice for the ii chord. However, I know of no minor scale that contains a dim7 in that position and have not heard of it used in that way before. I'm aware that the bb7 is the only difference between the two so does the substitution of the dim7 simply serve to add dissonance/tension/color?
Your choice here:
#3
Is there any certain context you would generally sub it in or just however you see sonically fit?
Your choice here:
#4
Quote by chewhat
Is there any certain context you would generally sub it in or just however you see sonically fit?


It's jazz, so pretty much anything goes.

Jokes aside, considering the fact that the ii chord is modified so often in jazz (especially into a Dom7), that tritone isn't exactly unusual for a ii.
#5
Yeah, take those chords apart and look at the voice leading:

Em7b5 = E G Bb D -> A7 = E G A C#

The Bb and D resolve down by step to A and C#

Now, if you make that ii fully diminished:

Eº7 = E G Bb Db -> A7 = E G A C#

There's only one tone that resolves, the Bb steps down to A.

To get a more authentically "jazz" sound, add sub out the root of the dominant for a b9, and see how that changes the voice leading:

E G Bb Db -> E G Bb C#

The same notes! So in that case, the resolution is really weak and you'd have to resolves you lines by changing other tones. BUT, you use the m7b5 alongside the dominant b9, you get:

E G Bb D -> E G Bb C#

Again, only that D needs to resolve.

So from this example, you can derive a simple "rule" for minor ii V i voice leading: You can use a half diminished ii when you also have a b9 on the dominant; and a fully diminished ii works if your dominant contains no b9.
#6
Quote by chewhat
Out of boredom I took another look at the II-V Jazz lines video by Andrew Wasson that's been on the homepage for some time now. As usual for him it was a good informative video but I noticed that one of his examples in D minor went Edim7-A7-Dm7. He went on to say that a m7b5 could also be used in place of the dim7.

My question is how/why does the dim7 work there? I know that for standard seventh chord harmonization of the natural minor scale the m7b5 is the harmonically "correct" choice for the ii chord. However, I know of no minor scale that contains a dim7 in that position and have not heard of it used in that way before. I'm aware that the bb7 is the only difference between the two so does the substitution of the dim7 simply serve to add dissonance/tension/color?

It's an altered V. The bb7 is the major 3rd of A7. The b5 is the b9 of A7.

So to summarise, it is nothing more than a rootless A7b9 in second inversion. Don't forget that dim7 chords are symmetrical.

It's also worth thinking about Joe Pass' approach to theory which only uses 3 different chord families, major, minor and dominant.