Dominant 7th Substitutions

[Nystul]

But why Edim for G7?

From the A section of Rhythm Changes:

Dm G7 Cm F7

you get

Dm Dbdim Cm F13

but Dbdim = Edim , so you arrive at

Dm Edim Cm F13

How is that functioning as G7 rather than Gm? I see there Edim as a fancy Gm with the E leading to the Eb of the next chord. If it went straight to F7 instead of Cm, then you could view it as a sub for C7. Diminished chords are very flexible. But taking a chord with Bb and E and substituting it for a chord defined by B and F... probably won't work in most cases?

[izonin]

But why Edim for G7?

From the A section of Rhythm Changes:

Dm G7 Cm F7

you get

Dm Dbdim Cm F13

but Dbdim = Edim , so you arrive at

Dm Edim Cm F13

How is that functioning as G7 rather than Gm? I see there Edim as a fancy Gm with the E leading to the Eb of the next chord. If it went straight to F7 instead of Cm, then you could view it as a sub for C7. Diminished chords are very flexible. But taking a chord with Bb and E and substituting it for a chord defined by B and F... probably won't work in most cases?

I don't know, it just sounds right in this case. But you can't substitute the F7 with a Ddim in this progression, 'cause it won't lead naturally to the Fm7 in the next bar.

[tapper mike]

Theories in jazz develop over time. They did not all come at once nor from one song. The Dominant 7th idea was not propagated with "I got rhythm". What was developed was the "ii=V"

The OP did not quote from "I got rhythm" he quoted from a book about a general idea regarding Dominant7 substitutions.

Un "The Complete Idiot's Guide To Music Theory" (that would be me) the author states "You can do diatonic substitution (using diminished chords a third above or below the dominant seventh)...". The example he gives is replacing G7 with Bdim or Edim. I understand why you can replace G with Em or Bdim. But why Edim for G7?

But if you look at a edim in a different stacking order you get a C7b9 no root.
(c)E-G-Bb-Db

[jancivil]

The OP did not quote from "I got rhythm" he quoted from a book about a general idea regarding Dominant7 substitutions.

Un "The Complete Idiot's Guide To Music Theory" (that would be me) the author states "You can do diatonic substitution (using diminished chords a third above or below the dominant seventh)...". The example he gives is replacing G7 with Bdim or Edim. I understand why you can replace G with Em or Bdim. But why Edim for G7?

edim [=] C7b9 no root.
(c)E-G-Bb-Db

Aaannd someone thought to bring in an idea from 'Rhythm Changes' to indicate how that move was in the 'A Section', to answer the OP's question, reiterated, 'why'.

Rhythm Changes is extrapolated from I Got Rhythm (unless there is a composition called 'Rhythm Changes')... I showed the actual A section of I Got Rhythm and where the conception arises: in the second phrase; where there is no substitute for V7. There is a #iv dim7, function is as a secondary dominant to ii. Very normal move. Not a substitution. V7 doesn't push to ii anyway. There is no sense to it.

'E dim' = C7 is kind of a non-sequitur as per 'substitute for G7'. If you want to show how that works, that context, fine. but it doesn't make for 'substitute for G7' in itself.

It is going to be problematic to prove that notion out of that book. so far the reasoning is flawed.

[jancivil]

Dbdim = Edim , so you arrive at

Dm Edim Cm F13

How is that functioning as G7 rather than Gm? I see there Edim as a fancy Gm with the E leading to the Eb of the next chord. If it went straight to F7 instead of Cm, then you could view it as a sub for C7. Diminished chords are very flexible. But taking a chord with Bb and E and substituting it for a chord defined by B and F... probably won't work in most cases?

I don't know, it just sounds right in this case. But you can't substitute the F7 with a Ddim in this progression, 'cause it won't lead naturally to the Fm7 in the next bar.

There ought to be a distinction made: you wrote E dim, which is E G Bb, when you meant E G Bb Db. So Nystul sees a Gm add6, where you mean more.

There can be reasons for that choice. However you exposed the flaw in the reasoning for it being G7 function by indicating it won't work for F7 did you not? E dim7 as dominant of Cm doesn't work.

except in convoluted modern jazz terms. Cf: Mike's C7; to Cm... it's been done, yes.

You can push harmony to that extent in jazz, but that structure does not per se substitute for a dominant, there are too many potential problems; "a chord with [tension tones] Bb and E substituting for a chord defined by B and F probably won't work in most cases".

[NKF]

The OP did not quote from "I got rhythm" he quoted from a book about a general idea regarding Dominant7 substitutions.

Un "The Complete Idiot's Guide To Music Theory" (that would be me) the author states "You can do diatonic substitution (using diminished chords a third above or below the dominant seventh)...". The example he gives is replacing G7 with Bdim or Edim. I understand why you can replace G with Em or Bdim. But why Edim for G7?

edim [=] C7b9 no root.
(c)E-G-Bb-Db

Aaannd someone thought to bring in an idea from 'Rhythm Changes' to indicate how that move was in the 'A Section', to answer the OP's question, reiterated, 'why'.

Rhythm Changes is extrapolated from I Got Rhythm (unless there is a composition called 'Rhythm Changes')... I showed the actual A section of I Got Rhythm and where the conception arises: in the second phrase; where there is no substitute for V7. There is a #iv dim7, function is as a secondary dominant to ii. Very normal move. Not a substitution. V7 doesn't push to ii anyway. There is no sense to it.

'E dim' = C7 is kind of a non-sequitur as per 'substitute for G7'. If you want to show how that works, that context, fine. but it doesn't make for 'substitute for G7' in itself.

It is going to be problematic to prove that notion out of that book. so far the reasoning is flawed.

I agree with you regarding the use of substitute Dom7 but i think if you just assume that most people mean a chord that approaches the tonic in a certain fashion that has a precedent ie has been heard before, perhaps a motion to another major triad, used to the tonic and given that we have the whole tonality thing still lingering, i think you are right but I'm pretty sure what people mean is a chord used to approach the tonic. I mean IV could be a substitute so i agree that the idea of a flat out substitute is assuming you need a dominant in the first place but it is kinda adding more complexity to the issue which i think is something one might think about later down the road. Or not.

[jancivil]

well the topic was substitute for dominant 7. and something from a source I'm not sure about.

one can say, 'iii subs for I in major', that kind of thing. All of this talk about chord progression qua itself ignores that most use of 'chord progressions' serves a melody. The reason for 'iii for I' isn't too interesting outside of what it does for the tune.

But this kind of thinking about IGR has a life of its own. I saw the wiki article on Rhythm Changes a coupla times... That dim 7th move (eg., in the second phrase of the original Gershwin*) had a lot of traction in the swing era but it got to be pretty cornball eventually.

*: that is a secondary dominant of ii. V does not function to that.

[NKF]

well the topic was substitute for dominant 7. and something from a source I'm not sure about.

one can say, 'iii subs for I in major', that kind of thing. All of this talk about chord progression qua itself ignores that most use of 'chord progressions' serves a melody. The reason for 'iii for I' isn't too interesting outside of what it does for the tune.

But this kind of thinking about IGR has a life of its own. I saw the wiki article on Rhythm Changes a coupla times... That dim 7th move (eg., in the second phrase of the original Gershwin*) had a lot of traction in the swing era but it got to be pretty cornball eventually.

*: that is a secondary dominant of ii. V does not function to that.

I think it is similar in say how the french 4/3 was an altered predominant but does it substitute for one or does it eventually become its own identity. I mean yes, it does come before V but then there are the versions that don't. Say using it in the same vein as the common tone diminished chord. You could even argue it is a passing chord. Does it substitute for ii b5 7 is just a matter of your own perspective and how you hear it.

Does an evade cadence substitute for a tonic ? In a way sure, but it is its own identity as well.

Which is why i think when learning, it isn't so bad to think of it that way because they did start out as substitutions. That french 4/3 final cadence in the intro to Finlandia which is pretty popular i'm sure most know it , had it not been there would of had a dominant.. ANd staying with that piece, the intro which follows the prescription of the G64 starting on the V64 which would normally go to F# avoids the standard G6 - V6/4 - D3 omnibus type voice leading so in that instance although it is using the device , it doesn't substitute to me at least as a predominant nor does the actual 6/4 chord resemble a V even tho it is using that device.

I think it is really up to the listener. Nobody could prove it is a substitute. But nobody could prove you don't hear it as such. For example, whenever i hear a half dimished chord going up a semi tone in say pre atonal music, I hear a V65 with the 9th of the chord as a suspension. That is just how i hear it. Makes mroe sense to me and i remember trying to argue it in class ages ago as it required less of a framework to create a new device but i soon realized , people hear things differently.