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The flat five substitution is the cornerstone of modern jazz. It is a change that goes back to Art Tatum, and more famously to Charlie Parker and the early Bebop players. It’s largely because of this sort of harmonic change, that swing players, like Louis Armstrong and Benny Goodman, called Bebop “Chinese music.” (Curious that Chopin used the same sort of progressions in developing his chromatic harmony, but no-one considers him the least bit Asian. Goodman, who was a thoroughly well trained, and brilliant, classical clarinetist, should have known better.)
First, lets notice that the b5 is the tritone. It is the most dissonant of all the diatonic intervals. As a result, the key that is furthest away from the key of C would be the Key of Gb(or F#). Thus, it seems intuitively obvious that these keys would have little relationship to each other.
The dominant chord in C is G7. Its spelled G B D F. It’s perfectly acceptable from the rule of alterations to play G B Db and F instead. This is a G7b5.
Now, lets look at the dominant chord in the key of Gb, which is a Db7. It’s spelled Db, F, Ab, and Cb. If we do the same alteration on this chord, we get Db F Abb and Cb. Now, Abb is enharmonically the same as G; and Cb is enharmonically the same as B. Thus, in terms of pitches, the Db7b5 chord is Db, F, G, B.
Lo and behold, the two are the same. A 7b5 chord has the same pitches as the 7b5 chord built a tritone away. Thus, you can substitute the one for the other.
Conservative rule – For any dominant seventh chord, you can substitute a dominant seventh chord with the root a b5 away. Thus for a D7 chord, you can substitute and Ab7 chord.
Here is one of the most common ways that this is done. For a ii V I progression, say Dmin G7 C, you substitute the b5 of the G7, and arrive at Dmin Db7 C. This creates a nice chromatic descending baseline.
Aggressive Rule For any chord, you can substitute a chord of the same character with the root a flatted fifth away.
In the same progression, you could play instead Ab min G7 C, this time substituting the b5 of the minor chord instead of the major chord.
Why does this work? Remember that several of our rules are reciprocal. So if you have for example a minor chord, you can first do a ii/V substitution on the minor chord, making it a 7th chord, then a b5 substitution on the 7th chord, and then another ii/V substitution. thus Dmin becomes G7 which becomes Db7 which in turn becomes Ab minor. (Also remember that you can turn a major chord into a minor chord with maj/min substitution, and then do this same procedure again.)
On the Guitar, this type of substitution is very easy to apply. Assuming roots on the 6th 5th or 4th string, the b5 is either up one string and up one fret, or down one string and back one fret. With just a little bit of practice, you should be able to start improvising these substitutions in your playing. But remember, they can easily lead to clashes with the melody, so you still need to exercise some care, and adhere to the primary rule: If it sounds bad, it is bad.
I am attaching two examples to this lesson. One is simply another version of Amazing Grace, incorporating the b5 substitution, along with everything else that I have covered (Extensions, Maj/minor, ii/V subs). With these few rules, you can see how jazzy the simple progression can start to become.
The second example is a simple four bar Ragtime blues progression: C A7 D7 G7. This sequence of chords appears very frequently, and the example shows the simple progression, then with extensions, and then three ways you could use b5 substitutions.
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Duffy P
This is basically a thank you posts for all the time and effort that you put in to providing in-depth background information about chord substitutions. I am currently reading each and every one of these posts; the going is a little slow for someone of my music theory level. Until now I have been reading a document I found on the Internet written in 1996 by Howard Wright titled: The Guide to Chord Theory – understanding chord construction and naming. I also have an ebook on Fretboard Theory written by Desi Serna. I am really having a good time trying to learn as much of this as I can while also applying this to my practice and playing. This afternoon I was practicing and starting working on some sheet music for jazz chords for the song Georgia. I still do not understand why the author of this work would use a fretted 4-note chord over a barre chord for some parts of this music, but I guess I will figure it out eventually. I have also been using a phone app called SmartChord to help in this endeavor.
I did not mean to get long winded on this but the subject matter itself is certainly that way. Thanks again Duffy P for your help in learning and understanding chord substitutions. Any more tips for assimilating chord theory and progressions are always welcome in my humble opinion. Great job! Cheers, Rip
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There are a few reasons why someone would prefer four fretted notes over a barre chord.
Number 1: Barre chords suck. I hate playing them and avoid them whenever possible. Seriously, I learned how to put my thumb over the neck, and rarely play barre chords anymore.
Number 2: Fretted chords allow you to create a more sparse voicing, which jazz players tend to favor. By the time jazz guitarists start playing in groups with a bass, and a piano, they start thinking about 3 note and even 2 note voicings. A big barre chord is just likely to step on the territory of either the bass or the piano.
Number 3: Very often, players want to be able to adjust a chord by changing only one note. Sometimes this is easier with a four note fretted chord than a barre chord, though not always.
Number 4: Did I say barre chords suck. Well they do.
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Well Duffy P, now you went and opened up a can of worms in terms of my own playing. By that I mean that if I have a particular cord where I am not getting a clean voicing or if the fingering on a particular chord is interrupting my tempo/rhythm, then I have been dropping a note out of the chord and playing a triad that essentially sounds like the full four-note chord. I did not know that this was kosher for jazz, but if I am reading your Note 2 above, then this is or may be a common practice? If so, you have just made my day! I have been spending time getting the barre chords programmed in my finger memory bank, but I would just as soon use some other voicing to accomplish the same end.
So, once again thanks for taking the time to share these playing tips with me. I might have mentioned in a previous post that I occasionally use my phone app SmartChord to look up another option for the fingering of a particular chord; it seems amazing that there are so many different ways to achieve either the same sound or an octave of that sound on the guitar neck! Any other tips that you can think of are always appreciated. Rip
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Not just jazz. Take a look at Brian’s early lesson on Steve Cropper. Also I think in a lesson on Keith Richards. Even if its not there, both of those guys would use triad voicings all the time.
Or listen to Bob Weir sometime playing rhythm for the Grateful Dead. Lots and lots of three and four note chords in his playing.
I’m pretty sure I could come up with a lot of other examples too, but those come immediately to mind.
The only other thing I would warn you against, is thinking that different ways of playing the same chord have the same sound. They will all fit in a simple chordal approach to the guitar. But play a G7 in open position these ways 320001 and 3×3003. Both are G7 chords, but they sound quite different. And that’s just one simple example.
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