Now, what about adding sevenths to augmented and diminished triads? When an augmented triad has a seventh added to it, it’s usually a minor seventh. Since the result is basically a dominant-seventh chord (because of the major third in the triad and the minor seventh on top) with an augmented fifth, the chord is called an augmented-seventh chord. Check out the Aaug7 below:

A-augmented-seventh chord

Chords like this are often used to heighten the drama of returning from V to I; for two examples from the classic rock canon, consider the last chord of the verse in both the Beatles’ "Oh Darling" and the Allman Brothers’ arrangement of T-Bone Walker’s "Stormy Monday."

A diminished triad usually has only a minor seventh added to it. You’d think the resulting chord would have the decency to be called a diminished-seventh chord, but it does not. It is called, instead, a minor-seven-flat-five chord, which is really just about the chord name to end all chord names. And yet, if you peel it apart, it does make sense. The minor third of the diminished triad and the minor seventh on top basically add up to a minor-seventh chord. But there’s the diminished fifth of the diminished triad. And a diminished fifth is a perfect fifth made a half step smaller, or flatted. So, a minor-seven-flat-five chord is just trying to tell you: "I’m a minor triad with a minor seventh added. Oh, and by the way, my fifth has been flatted as well." This takes up too much room on the page, so it’s written m7b5. Now you know what that means. Try the Am7b5 below.

A-minor-seven-flat-five chord

There is such a thing as a diminished-seventh chord. It's a diminished triad with a diminished-seventh interval added to it (a diminished seventh is a minor seventh that’s been made one half step smaller). So it makes a certain kind of sense: a maj7 chord is a major triad plus a major-seventh interval, a m7 chord is a minor triad plus a minor-seventh interval, and a dim7 chord is a diminished triad plus a diminished seventh. Try out this Adim7:

A-diminished-seventh chord

One essential use for a diminished chord is as a connection between I and ii; try Example 3, in which you connect D and Em by way of a D#dim7 chord.

Example 3

So as we’ve seen, the chord names are just trying to tell you what’s there. Next month, we’ll venture further into chord terminology, demystifying sixth, five, sus4, ninth, and 13th chords and tangling with maj6add9 and 7b13#9 chords.

[To continue on with Part 2 of this lesson, click here.]

FROM THE BOOK The Acoustic Guitar Method Chord Book from String Letter Publishing/Hal Leonard (www.stringletter.com)