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I'm going through Garrison Fewell's "Jazz Improvisation for Guitar - A Harmonic Approach". The start of Chapter 1 reads:

Triad substitution is the use of triads derived from the chord tones and melodic extensions of a chord, beyond the basic triad. These triads can be categorized as either diatonic substitutions (triads that only contain chord degrees 1, 3, 5, 6, or 7) or upper-structure triads (triads that contain at least one tension)

So, in Cmaj7 Lydian we have:

  • Chord tones: C, E, G, B

  • Tensions: D, F#, A

Which means:

  • Diatonic substitutions: Em, Am

  • Upper-structure triads: G, Bm, D

  • F#dim is an upper-structure triad but is unstable and not used as often

How does this translate to minor chords? Let's say I want to know the diatonic substitutions and upper-structure triads of Am7 in Dorian mode.

  • Chord tones: A, C, E, G

  • Tensions: B, D, F#

Now, C is one diatonic substitution, and the other seems to be F#dim (F# A C), but I don't hear it as "compatible" as the other diatonic subs (if that makes sense?), so I'm not sure about that one. The upper-structure triads would be Em, G, Bm, D.

Is this correct? For minor chords, the triad diatonic substitution and upper-structure triads are derived in the exact same way as in major chords? (And in a related note, in the Ionian and the other 6 modes derived from it, are there always two diatonic substitution triads?)

  • I'm not familiar with the book. Are the substitutions substituting notes within a chord or one chord for another? – Josiah May 14 '15 at 12:00
  • @Josiah I didn't know the concept was too vague. Sorry about that. It's about triads that can be played melodically while on a given mode. – Jamm May 14 '15 at 13:37
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As for the sound of the F#dim chord, I would guess that the reason it doesn't sound compatible is that F# is the one note where A Dorian differs from vanilla A Minor. It's not in our "normal" musical system to have only a raised 6th in a minor key, so having a diminished chord build on that note is out of our common experience.

My assumption is that this is a system of substituting one chord for another.

Though I am not familiar with that book or the terminology, I would expect, based on the excerpt, that in C Lydian the chord tones would be C E G A B, and the tensions would be only 2 and 4 (D and F#). So your upper structure triads would be G, b, D, and f#dim. If my assumptions are correct, your diatonic substitutions would be an e or an a, which makes sense harmonically - you could use the e or the a in place of a C and it would be ok.

You should be able to do the same with any chord - for example, a G chord in C Lydian would have the chord tones G a B c D E F#. Substitutions: b and e. Sounds good to me.

In A Dorian, we'd have A b C d E F# G (tensions are lowercase), so the upper structure triads will be e, G, b, and D. A chord built on F# would be a diatonic substitution (given the mode), but it will sound weird. The other diatonic substitution would be C.

If the system is meant to be extended beyond triads, then we can determine what quality of 7th chord we can use in the substitution. In A Dorian, it's a fully diminished f#7. In C lydian, it's a minor minor a7.

Like I said, I'm unfamiliar with the work and the terminology, but that's how I would understand the system. What I don't get is why we don't just say "you can substitute the chords a diatonic third away." So take this analysis with a pinch of salt and maybe some paprika.

  • The chord tones, tensions, diatonic subs, and upper-structure triads in C Lydian that you see in the question are examples from the book. Those were not my interpretations of the lesson. Those are the actual tensions and diatonic subs according to the book. My doubt is regarding A Dorian, how those examples translate to Aeolian or Dorian. – Jamm May 14 '15 at 13:32
  • Hrm. I guess I don't understand then. Guess you'll to wait for somebody who knows the book. :) – Josiah May 14 '15 at 21:57
  • I really appreciate your time and help. – Jamm May 14 '15 at 22:58
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To me it just seems to be saying you take the chord/scale, whatever that happens to be, and any triads you can build from that chord/scale can be used in place of the 7th chord built from its tonic.

What type of chords those will be will just depend on the chord/scale.

It's really just seems to be a heuristic for voicing the chord/scale.

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The quick answer is --> yes, minor chords work the exact same way as major chords. You've noticed that a dim chord doesn't "work" very well. The reason is that there is a tritone in a diminished chord, which can clash and sound off if used.

Another way to get a handle on the idea and feel of this is to create the chord, say w/ the upper extension chord superimposed:

eg: Amin7 played w/ Bmin. This is going to give you A C E G + B D F# (which is basically the whole chord scale). Analysed the chord is going to be: Amin7(9/11/13). Pretty much the kitchen sink.

--> random: I went to Berklee, and Garrison Fewell was teaching there at time (not sure if he still is). He is a MONSTER player! Amazing.

(Incidentally, at least at Berklee, a "tension" is defined as being a major 9 above a chord tone. So Amin = A C E, the tensions of that chord are then going to be: B D F#. The "guitar/harmony thinking for dummies" that I used to get through school? Just a whole step above the chord tone. Sometimes you'll hear the word "extension" instead of "tension". To me they essentially mean the same thing. Others will argue, but I put the playing ahead of the theory arguments for simplicity sake.

-- Example--> should you play #11 over a minor7 (this can be non-diatonic, depending on how you are thinking), or natural 11?)

A better way to start using these is to omit some of the notes. The fifth is usually omitted. You could also think of the chord being:

Bmin/A --> But you do want to include the b3 (C in this case) to make sure there is a minor feel to the chord. A lot of this winds up being implied, and your ear and listener's ear will "hear" Amin7.

Try different inversions and see how they sound. Also, as is case w/ diminished chords, you have to use care w/ upper extensions. If you play Bmin over Amin7 you have these two notes: C F# . This can sometimes make a weird/unintended dominant chord feel, ie, you could sound like you're playing D7 instead of Amin7.


Another source to look at is

  • Mick Goodrick's "The Advancing Guitarist".

Deceptive in that it is written in pretty simple style, but it literally bottomless ideas that will keep you busy for rest of your life. Yet another great book on chords/harmony that is really practical is:

  • Steve Khan "Chord Khancepts" Lots of ideas that you can immediately implement into your playing

Bonus.

7th chords can be played over roots too. A beautiful way to play an Amin9 is to play drop 2 Cmaj7, 2nd inversion (E B C G) over an A root.

As always, your ear is the final judge of what sounds good, choices you like. All of this is meant to be a guide for you to map out and explore.

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