Sep 29

The blues have a certain love affair with the flatted interval. Somehow, the tension created by both a major and minor 3rd interval lies at the heart of the blues. Classical theory shies away from such tension and color, instead using 4ths and 6ths to create the common color.  Today I would like to talk a bit about the different uses of tension intervals by mixing major and minor 3rd invervals.

Stacking 3rds: Common Chords

Before we start, the idea is to stack 3rd intervals, either major or minor, to create chords. Here is an example:

  • I to III: is this a major or minor chord?
  • III to IV: returns to a fifth
  • IV to VII: is this a dominant seventh or a major 7th chord?

A unique aspect of blues, and later jazz, is how the 3rds stack. Lets look at a standard C7 chord: C E G B♭. If we take each two subsequent intervals and examine them, we get this.

  • C to E: a difference of a major 3rd (resulting in a major chord)
  • E to G: a difference of a minor 3rd
  • G to B♭: a difference of a minor 3rd (resulting in a dominant seventh chord)

So, by stacking a major, minor and minor we get a dominant 7th chord (or just plain 7th chord, whichever terminology you prefer). The first stacked interval (C to E) dictates whether the chord is called major or minor.  The second interval (E to G) brings it back to the fifth and is the opposite of the first. And the third interval (G to B♭) dictates whether it is a dominant 7th or a major 7th.

I suggest we look at a Cm7 chord now: C Eb G B. Again, we will take each two subsequent intervals and examine them, resulting in:

  • C to E♭: a difference of a minor 3rd (resulting in a minor chord)
  • E♭ to G: a difference of a major 3rd
  • G to B♭: a difference of a minor 3rd (resulting in a dominant 7th)

I hope you can see the connections between the intervals chosen and the quality of the chord. Let’s try a Cmaj7 chord: C E G B.

  • C to E: a difference of a major 3rd (making this a major chord)
  • E to G: a difference of a minor 3rd
  • G to B: a difference of a major 3rd (making this a major 7th chord)

Stacking 3rds: Jazz Harmony

When you get involved with jazz, you get involved with some more interesting harmony. It is not, however, that difficult at all to understand. Lets try stacking some different 3rds and maybe an extra one on top.

Let’s look at a common Cdim7 chord: C E G B. Don’t let the B♭♭ confuse you, its just the proper way to flat a B♭. It’s really an A.

  • C to E♭: a difference of a minor 3rd (making this a minor chord)
  • E♭ to G♭: a difference of a minor 3rd (making this a diminished chord)
  • G♭ to B♭♭: a difference of a minor 3rd (making this a fully diminished chord)

So a fully diminished chord is simply a bunch of stacked minor 3rds. Pretty easy huh? Let’s try a close cousin, the Cm7(♭5) chord: C E Gb B. This is also called a half-diminished chord.

  • C to E♭: a difference of a minor 3rd (making this a minor chord)
  • E♭ to G♭: a difference of a minor 3rd (making this a diminished chord)
  • G♭ to B♭: a difference of a major 3rd (making this a half diminished chord)

Let’s take a short step back and then take two steps forward to add a 9th to our chords. For a regular 9th chord, you use the dominant 7th as a base and add yet another third. Alas, a C9 chord: C E G B♭ D.

  • C to E♭: a difference of a minor 3rd (resulting in a minor chord)
  • E♭ to G: a difference of a major 3rd
  • G to B♭: a difference of a minor 3rd (resulting in a dominant 7th)
  • B♭ to D: a difference of a major 3rd (resulting in standard 9th)

Taking that second step forward, lets try out a funnier chord. Here is a C7(♭9) chord: C E G B♭ D♭. Everything else is the same except the final interval:

  • C to E♭: a difference of a minor 3rd (resulting in a minor chord)
  • E♭ to G: a difference of a major 3rd
  • G to B♭: a difference of a minor 3rd (resulting in a dominant 7th)
  • B♭ to D♭: a difference of a minor 3rd (resulting in flatted 9th)

The usefulness of these chords is best learned through experience, for example, 7(♭9) chords work great as the V chord before coming back to the root.

The idea is to imagine chords as building blocks. There is no mystery as to how they are constructed. Spend a little time with a piano and get the feel for the correct changes and you’ll pick it up in no time.

This is an archived version of the website.

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