question about chord substitutions

[pula58]

Let's say we're playing a blues: C7, F7 and G7.

I am familiar with substituting a, for example, B7 chord for the IV (F7) chord (a flat five sub, sometimes called tritone sub).

But, what about the V chord (the G7). What is a good subsitution for that?

[gennation]

Play a m7b5 chord from the M3 of the 7th chord, like Bm7b5 for a G7 chord. It ends up being a rootless G9 chord. This is very T-Bone Walker-ish.

You can use the sub for almost any 7th chord.

So for G7 C7 and D7 play Bm7b5, Em7b5, and F#m7b5 respectively.

[docbop]

What's note is a tritone up from G???? The answer will be the root of the 7th chord you want.

Hint you will create a nice chromatic root movement back to the I C7.

[Cainer]

Depends on which part of the blues progression you're at. If you're resolving back from the V to the I, use any chord built off the melodic minor a half step up from the V. For instance, on G7 which resolves back to C, you could substitute any chord from Ab mel minor: Abminmaj7, Bbmin7, Bmaj7#5, Db7, Eb7, Fmin7b5, or Gmin7b5. An easy way to get started is just think dominant 7th on the b5 or #5 relative to the dominant chord of the moment. Keep in mind this only really works if the 7th chord is resolving up a 4th, so G7 to C, E7 to A, etc. In a blues it works when you go from the I to the IV, or from the V to the I.

You can also just use a minor pentatonic built off the b3 of the 7th chord you're playing over, which gives you the altered tonality without having to learn a new fingering/scale.

What I'm describing above are ways to get an altered sound, which adds lots of tension and begs for resolution.

If you don't want to get an altered sound, i.e. the chord doesn't resolve up a fourth, you can substitute a maj7 chord built a tone lower than your dominant7 chord quite nicely. So if you're vamping on C7, try using a Bbmaj7 arpeggio. If you consider the dominant 7th chord to be the V chord in a major key, you can substitute any chord from that key over it, with varying levels of success. So over a G7, any chord from the key of C major will give you some sort of different colouring.

Hope that helps more than it clouds the issue, and always remember that rules were made to be broken!

[JonR]

Originally Posted by pula58

Let's say we're playing a blues: C7, F7 and G7.

I am familiar with substituting a, for example, B7 chord for the IV (F7) chord (a flat five sub, sometimes called tritone sub).

That's not a good sub because the F7 is not acting as a V7 chord.
(At least, I've never seen a tritone sub used on a IV chord in blues.)
I actually don't think there's much you can do on bar 5 of a blues. It pretty much has to be the IV chord. Even Charlie Parker (king of subs!) didn't change bar 5. It stops being "blues" if you do, that's the point.
But you can mess with bar 6, before it goes back to I. The most common changes in bar 6 are either the #IVdim7 (F#dim7) or the minor iv (Fm). Both these chords lead back quite well to C - although the Fm doesn't go so well to C7 as F#dim7 does.
You could even try a bVII, Bb7

Originally Posted by pula58

But, what about the V chord (the G7). What is a good subsitution for that?

Because that's the V chord, a tritone sub is valid there. It would be Db7 - however, not if the G7 is leading to F7!
The point being that a tritone sub is designed to lead straight to the tonic - or to sub for a secondary dominant resolving the same way.

So in a jazz blues, where the last line goes Dm7-G7-C-C, you can sub Db7 for G7 there. But in a rock blues, Db7-F7-C is going to sound wrong. (And Db7-B7-C even weirder!)

A common place for a tritone sub in blues is as the I goes to the IV. So, in bar 4, maybe on the last 1 or 2 beats, instead of C7 you can play Gb7. This obviously slides down a half-step to F7. (Tritone subs always need to do that - IOW, instead of V7, they become bII7.) In this case, C7 is acting as a secondary dominant ("V/IV", dominant of the IV chord).

The most common kinds of sub in blues (or rather, harmonic embellishments) are kinds of "backcycling" - introducing more secondary dominants, and sometimes secondary supertonics (ii chords).

Eg, to get to F7 in bar 5, you can play Gm7-C7 in bar 4 (ii-V of IV). And you could use tritone subs for both those: Dbm7-Gb7
To get to a Dm7 in bar 9 (we're talking jazz-blues, right?) you can play an A7 before it, and maybe an Em7b5 before that. (Em7b5-A7 = ii-V in D minor).
In the last 2 bars of a blues, you commonly get backcycled turnarounds. Eg, in key of C, bars 11 and 12 might run C-A7-D7-G7, or C-A7-Dm7-G7, or C-Am7-D7-G7, etc.
And you can use tritone subs there too, giving you all these options in those final two bars:
C-A7-Ab7-G7
C-A7-D7-Db7
C-Eb7-D7-Db7
C-Eb7-Ab7-G7
etc.

A common blues ending (end of last verse) is to use a bII-I instead of V-I. 9ths are especially good for this: end a C blues with Db9-C9.

A real tour de force of subs in a blues is Charlie Parker's "Blues For Alice" - you really can't go much further than this - and you probably wouldn't want to go even this far! (The original is in F, but I'm transposing to C for comparison with the above).

|Cmaj7 - - - |Bm7b5 - E7 - |Am7 - D7 - |Gm7 - C7 - |
|F7 - - - |Fm7 - Bb7 - |Em7 - A7 - |Ebm7 - Ab7 - |
|Dm7 - - - |G7 - - - |C - A7 - |Dm7 - G7 - |

Notice the long cycle of 5ths from bar 2 to bar 6: B-E-A-D-G-C-F-Bb. (These could all be dom7s, but an alternation with m7s makes for a smoother sequence.)
Starting from the Fm7 is a run of ii-V pairs descending chromatically. You could regard the Ab7 as a tritone sub for D7, preceded by its ii chord.
An optional extra sub is Em7 for C in bar 11 - which means you'd only get the tonic chord in bar 1! (And also notice that's a maj7, not a dom7.)

In a minor blues, btw, you can get other kinds of subs. Eg, you can sub the minor iv chord with the bVI7.
So a blues in C minor can go to Ab7 instead of Fm in bars 5-6.
And bars 9-10 can use bVI7 to V7 instead of ii-V:

|Cm7 - - - |Cm7 - - - |Cm7 - - - |Cm7 - - - |
|Ab7 - - - |Ab7 - - - |Cm7 - - - |Cm7 - - - |
|Ab7 - - - |G7 - - - |Cm7 - - - |(Dm7b5 - G7 - )|

You can hear that funky bVI chord in bars 5-6 in Horace Silver's "Senor Blues" and in Herbie Hancock's "Canteloupe Island" (not really a blues in total, but it begins like a minor blues).
The bVI-V in bars 9-10 is very common (in fact, standard in a minor blues), and you could also try it in a major key blues. (You often get it in Stormy Monday, eg.)
Minor keys rarely get fancier subs than these, perhaps because minor tonalities are weaker than major, and can't take too much alteration. (If you were to stick with Fm7 as iv, you can play a C7 in bar 4 before it, and maybe even a Gm7b5 before that. Gm7b5-C7 is the normal ii-V in F minor.)

[HassanBinSober]

Funny how some guys know all of this stuff and others just play the same few rock licks they learned in high school.

[Rob 62]

Jon - great post. Worth printing.