role of IVdim

**flyingace** · 02-24-2014, 08:18 PM

Often in a Blues progression, the movement from IV back to I is punctuated with a IV#dim chord. For instance, G7 to C7, C#dim, G7.

While the strong relationship between the C#dim leading to G7 in unmistakable, I don't get it. What creates this strong tension? It can't be a V7 to I because C#dim7 has a C# (maj 7 of D). What harmonic role is the dim chord playing?

**fep** · 02-24-2014, 08:26 PM

I remember there was some classical theory regarding this but I don't remember the details.

But it is a distinctive and cliche sound and that works pretty well for me (in other words, I'm not too concerned about using the theory to help me categorize it on this one since it's easy to hear).

If you look at these voicings:

x3535x - C7

x4535x - C#dim7

x5546x - G7/D

Looking at that, the C#dim7 is just a C7 but replace the root C with a C#, and the C# is a chromatic passing tone taking you from the C7 to the G7/D. And, it's some pretty smooth voice leading.

**AlsoRan** · 02-24-2014, 10:10 PM

You are asking about the C7 to C#dim7 to G7, right?

First, let's explain the tension. Fareed Haque and many others teach that Dom7 and Dim7 chords are chords of movement, so you could say the tension is never fully resolved when you use only these types of chords in a progression, as in a Blues.

Now for the progression.

First, notice the shared chord tones between C7 and C#dim 7
C7 and C#dim7 both have the same 3rd, which is E, and the same 7th, which is Bb, and the same 5th, which is G.

So the only chord tone to move is C to C#. That movement is a 1/2 motion.

Now for the other movement, C#dim7 to G7.

It is just a matter of recognizing that the diminished 7th of C#dim7, which is Bb, moves up a half step to B, and becomes the major 3rd in G7. And the third of C#dim7 moves a half step to F, and becomes the 7th of G7.

I am sure you know that the 3rd and 7th define a chord's quality, as in Dominant, Major, or Minor - so they are your most important chord tones.

Finally, you can also look at the C# moving a half-step to D, and becoming the 5th of G7 (it was the root of C# dim7) and the 5th of C#dim7 is shared with the root of G7, which is of course, G.

Hope this helps and you can see the motion of the individual notes in the chord progression.

**JonR** · 02-25-2014, 05:44 AM

Yes, it's about the voice-leading, particularly in the bass. Typically the following I chord will have the 5th in the bass, continuing the chromatic rise - C-C#dim7-G/D - which might then go on up (via B7/D# or D#dim7) to E7 (V/ii).

AFAIK, the classical term is "common tone diminished", relative to the following chord (contains the root note of that chord). IOW, in that view, it's really a Gdim7.
(Happy to be corrected on that

)

**Little Jay** · 02-25-2014, 09:42 AM

Could you view the C#dim as a C7b9 with the b9 as a bass-note? (C7b9/Db also)

**flyingace** · 02-25-2014, 10:26 AM

I guess I'm looking for an explanation in terms of common (III VI II V I) harmonic movement. That's why I try to see the C#dim as some kind of D7. But it just doesn't add up.

Just from playing the chords, the C#dim has a very strong resemblance to an A7 (C#dim = A7b9). If you play A7 to G, it sounds very similar. If you play C#dim to D7 to G, it sounds like a standard II V I progression. I think the connection is just a stronger II7 to I, bypassing V.

I don't say this with any authority. Just throwing it out there...

**randalljazz** · 02-25-2014, 10:42 AM

Originally Posted by JonR

Yes, it's about the voice-leading, particularly in the bass. Typically the following I chord will have the 5th in the bass, continuing the chromatic rise - C-C#dim7-G/D - which might then go on up (via B7/D# or D#dim7) to E7 (V/ii).

AFAIK, the classical term is "common tone diminished", relative to the following chord (contains the root note of that chord). IOW, in that view, it's really a Gdim7.
(Happy to be corrected on that

)

tricky biz (ex. i is approx our case here):

http://mailer.fsu.edu/~nrogers/Hando..._7_Handout.pdf

**fep** · 02-25-2014, 11:01 AM

This song is usually in Bb but I bet you can guess what it is (an excerpt done in our key in this thread - G):

| G6 / G9/B / | C7 / C#dim7 / | G/D / D7 / | G6 / / / ||

|| B7 / / / | / / / / | E7 / / / | etc.

Very cliche, right?

3x243x - G6

x2323x - G9

x3535x - C7

x4535x - C#dim7

x5543x - G/D

x5453x - D7

3x243x - G6

Good voice leading.

**JonR** · 02-25-2014, 11:41 AM

Originally Posted by randalljazz

tricky biz (ex. i is approx our case here):

http://mailer.fsu.edu/~nrogers/Hando..._7_Handout.pdf

Thanks. "approx", as you say, because the neighbouring chords are I and V rather than IV and I. But I guess it's close enough.

**kenbennett** · 02-25-2014, 11:44 AM

Originally Posted by Little Jay

Could you view the C#dim as a C7b9 with the b9 as a bass-note? (C7b9/Db also)

I see it more as a rootless A7b9

**monk** · 02-25-2014, 01:16 PM

I agree with Frank. Voice leading.

**JonR** · 02-25-2014, 01:28 PM

Originally Posted by kenbennett

I see it more as a rootless A7b9

I agree, but really it's just C#dim7. Not every dim7 is a sub for something else...

**JonR** · 02-25-2014, 01:36 PM

Originally Posted by flyingace

I guess I'm looking for an explanation in terms of common (III VI II V I) harmonic movement. That's why I try to see the C#dim as some kind of D7. But it just doesn't add up.

Right - it's nothing like D7! (not one single note in common)

Originally Posted by flyingace

Just from playing the chords, the C#dim has a very strong resemblance to an A7 (C#dim = A7b9). If you play A7 to G, it sounds very similar. If you play C#dim to D7 to G, it sounds like a standard II V I progression. I think the connection is just a stronger II7 to I, bypassing V.

I don't say this with any authority. Just throwing it out there...

Yes, it's tempting to try to see any dim7 as some kind of dom7 sub. It's a jazz habit.

But they don't always work like that. Dim7s have three possible actions, only one of which is vii (equivalent to a rootless V7b9).
But going with that notion, it is possible - given that the G in this context often has a D bass - to hear the G/D as what classical theorists call a "6/4", which is something like a Dsus chord. And the fact that the G does go to D after a couple of bars almost supports that.
So you could - just - argue that C#dim7 is a "secondary leading tone chord" (vii/V, vii of D), just with a delayed resolution, preceded by G/D as a kind of Dsus sound.

But seeing as we have the option of the "common tone diminished" interpretation - relating directly to G - we don't need to go that far. (see randall's link, if you haven't already.)

And actually all we really need to see (and of course hear) is the voice-leading, as mentioned - how chord tones slip up or down to the nearest note on the next chord. Every functional chord change works that way. Identifying function is a kind of secondary game.

**monk** · 02-25-2014, 01:47 PM

Sometimes a diminished chord is simply a diminished chord and sometimes we overthink things un-necessarily.

**flyingace** · 02-25-2014, 03:40 PM

Originally Posted by monk

Sometimes a diminished chord is simply a diminished chord and sometimes we overthink things un-necessarily.

I admit to being handicapped in this way. It took me so much longer to learn the guitar because everything had to be pigeon-holed and fit my pre-existing theoretical framework. Problem is, if it doesn't make sense or 'fit', I don't remember it. So I try hard to bring order into an art form - might as well herd cats.

**monk** · 02-25-2014, 04:00 PM

Originally Posted by flyingace

I admit to being handicapped in this way. It took me so much longer to learn the guitar because everything had to be pigeon-holed and fit my pre-existing theoretical framework. Problem is, if it doesn't make sense or 'fit', I don't remember it. So I try hard to bring order into an art form - might as well herd cats.

I hear you. I used to be the same way. The hardest thing I've had to do is unlearn all the so-called "correct' stuff I learned as a beginner out of books and magazines and get down the nuts and bolts of how the Real Players play Real Music. That meant time spent in clubs and at concerts with eyes and ears wide open.

**wizard3739** · 02-26-2014, 01:33 AM

My ear tells me it is a nice passing chord and can be played without thinking about it.

wiz

**Cunamara** · 02-26-2014, 11:49 PM

This chord is usually functioning as a chromatic bass line. That's usually all there is to it.

**cosmic gumbo** · 02-27-2014, 07:56 AM

Originally Posted by Cunamara

This chord is usually functioning as a chromatic bass line. That's usually all there is to it.

That's it, it's just bass voice leading.

**randalljazz** · 02-27-2014, 09:19 AM

Originally Posted by cosmic gumbo

That's it, it's just bass voice leading.

but if you understand the chord, then you will see many more possibilities than the serendipitous half step bass movement (from post #2):

x3535x
x4535x
x5546x

as:

x3535x
x1202x
x2303x

or:

xx2333
xx2323
xx0201

or:

xx8988
xx89109
xx9101010

**flyingace** · 02-27-2014, 10:51 AM

My view has ended up being that a dim chord is used most often as a bridge between two chords that don't have inherently good voice leading. I think this is due to it being symmetrical (each tone can the root). Pretty easy to find a 'connection' to the next chord when you have 4 roots work with.