Diminished chords and the blues

The blues is a good entry path for beginner guitarists. If you learn the standard fifteen chords and the blues scale, you’ll be well on your way. However, there’s one crucial piece of additional music vocabulary you need to fully inhabit blues tonality, and that is the mysterious diminished seventh chord.

To make a diminished seventh chord, you start on any note, go up a minor third, then another, then another. Here are the notes in Cdim7:

You can also derive this chord from C7: take each note in the chord except for C and slide it down a half step.

This video explains how dim7 chords relate to other seventh chords. Here are some good guitar fingerings for dim7 chords.

Diminished chords are highly symmetrical, which gives them a peculiar property. The circle above shows C diminished, but the same notes also make Eb, Gb and A diminished. The only difference between these four chords is their respective bass notes.

Diminished chords sound great in the blues. Three out of the four notes in the diminished seventh chord are notes in the blues scale:

Three out of the four notes are also found in the major blues scale:

You can play both blues scales using the aQWERTYon.

Any time you have an uninterrupted stretch of C7, you can liven it by dropping briefly to Cdim7 and then sliding back up to C7. Robert Johnson did this a lot on the first four bars of twelve-bar blues.

In “Kindhearted Woman Blues“, you can hear this riff on the line “Now there ain’t but the one thing that makes Mr Johnson drink, I swear by how you treat me baby, I begin to think.” Listen at 1:16. (He’s playing in Bb, not C.)

Diminished seventh chords also form part of a ubiquitous blues and jazz lick that I know as the Blue Monk lick, from the classic Thelonious Monk tune.

There are a few variations on the Blue Monk lick:

You can freely insert the Blue Monk lick anywhere you have two or four bars of a single dominant chord. For example, Fats Waller uses it  in the bridge of “Honeysuckle Rose,” under the line “You’re my sugar.” Here’s a live version by Ella Fitzgerald and Count Basie, listen at 2:12.

The Blue Monk lick works equally well backwards, particularly as an ending:

Wikipedia calls this the “How Dry I Am” lick, but I associate it more with Bob Dylan’s “Rainy Day Women #12 & 35.”

Another good use for diminished chords in blues and jazz is to follow the IV chord with the #IVdim7 on the way up to V or I. In C, you can play F7, then F#dim7, then either G7 or C/G. I mentally refer to this riff the “gospel lift.” Use it in bar six of the twelve bar blues and feel the spirit. Jazz also loves the gospel lift. Hear it in Duke Ellington’s “In A Mellotone” as sung by Lambert, Hendricks and Ross — listen at 1:03.

The gospel lift also shows up in a turnaround commonly used in bars eleven and twelve of twelve-bar blues, and as an ending.

The other major use case for diminished chords is for dominant chords in minor keys. In D minor, the dominant chord is A7(b9). You can think of this chord as being a C#dim7 chord with an A underneath it. If you’d like, you can also just leave out the A entirely. You can use this as a secondary dominant for minor chords, and make a nice chromatic bassline in the process. For example:

This isn’t blues, but the Roots use the minor-key dominant diminished idea heavily in their song “Don’t See Us.”

So go for it, blues musicians, use those diminished chords!