For centuries, diminished chords have been used to invoke a feeling of terror. From the earliest Italian operas to horror movies of today, the ascending diminished chords in Ex. 1 have had us scared out of our minds. It’s a cliché, but it’s a good cliché.
Out of context, diminished chords can sound a bit ambiguous—you probably wouldn’t vamp on a diminished chord for any extended period of time like you might on a dominant-7th or minor chord. But if you’re looking for that perfect “connector chord” to spice up two potentially boring chords, then this diminished business might be just the ticket.
A little background: A diminished chord is constructed of stacked minor thirds. As we see in Ex. 2, the melodic distance from the root to the b3 is a minor third interval (or three half-steps), from the 3 to the b5 a minor third, and from the b5 to the bb7 (double-flatted, or diminished, 7) a minor third. If you were to stack yet another minor third on top of the bb7 you’d land back on the root, one octave higher.
Because of this perfect symmetry, moving the entire chord up or down a minor third results in a different inversion of the chord—and with no new fingerings required! Just move the shape exactly three frets up or down and you have the same four notes every time, as proven by Ex. 1. Therefore, Cdim7, Ebdim7, Gbdim7, and Adim7 are really just inversions of the same chord. This means that in the entire 12-tone system of Western music there are only three different diminished-7th chords.
OK, there’s the theory, now let’s make some cool sounds.
The most common way composers use the diminished-7th chord is as a means to liven up otherwise boring V-I cadences. Here’s how it’s done: Instead of playing the functioning dominant chord (that is the dominant-7th chord that, acting as the V chord, resolves to the I chord), simply play a diminished-7th chord a half-step higher. Followed by the I chord, this new chord creates a richer, more complex sounding harmonic resolution. And, while you could look up fingerings for diminished chords in a book, the sly way to perform this entire process is simply to raise the root of your original dominant-7th chord a half-step (without changing any of the other notes).
In Ex. 3 we see a II-V-I progression in Cm. This sound is heard in countless jazz and Latin tunes. To zest this up with some diminished action, check out Ex. 4. Here, we have the same progression but, with Abdim7 substituting for the G7. This chord sub not only creates smoother, more intriguing voice leading, but it’s also easier to play than Ex.3 and will make you sound like a master on your next solo acoustic performance. For extra pizzazz, you can move the diminished chord up or down three frets at a time before resolving to the I chord—in this case Cm7—as shown in Ex. 5.
To apply diminished passing chords to the I-VI-II-V (Cmaj7-A7-Dm7-G7) progression in Ex. 6—a staple of hundreds of standards and show tunes—give Ex. 7 a listen. Here, we add lively new colors by using diminished subs for the two dominant chords, A7 and G7. By the way, these substitutions can be used without even telling your bass player what you’re doing, because they’ll work perfectly well with the original bass notes. Why? Because if you play Abdim7 and add a G in the bass, your listeners hear the composite chord: G7b9—which is a tasty and timeless resolution to Cmaj7.
While diminished chords often resolve up a half-step, Ex. 8 shows how they can work resolving down a half-step as well. This is a bossa nova phrase, so it is best played fingerstyle with the picking-hand thumb in charge of the bass notes. Thanks to its liberal usage of open strings, this example is especially beautiful—and very acoustic friendly. And, like every other example in this lesson, the diminished chords remind us that it’s not always where you go that counts, but how you get there.