Diminished Understanding

[Michael L]

I recently heard an explanation of diminished chords that, to my mind, made them much more accessible and useable. I’ll attempt an explanation here, and I hope this is useful not only to my fellow “theory nerds”, but also those who just want to play some music.

If you just want the take-away, jump to the end… but it might require the steps along the way to understand it. It’s not really heavy theory, just intervals and how chords/triads are built. I’d encourage you go step-by-step and stick with it. I think the payoff is worth the journey. Here goes…

Dominant Chords
I think most of us understand dominant chords, that is, a V7 resolving to a I chord in a key. G7 to C, A7 to D, etc.
The dominant chord is a tension chord within the key that resolves to a specific target chord.

Secondary Dominants
While the V7 to 1 keeps us within a key, we can always borrow a dominant 7 chord from another key to resolve to a chord other than the I. Every chord has a dominant, that is, a chord based on the 5th degree of it’s own scale. For example, if we are in the key of C and moving from the I to the iii chord, C to Emin, we could preceded the iii chord with its V7 from the key of E giving us C B7 Emin. The B7 is the tension chord resolving to it’s particular target, the Emin. We choose the tension chord based on the target.

Dominant to Diminished
Looking at a dominant chord we find the intervals Root 3rd 5th and flat 7th. The 3rd, 5th, flat 7th form a diminished triad over the root bass note. A G7 chord, for instance, is G B D F. You could think of that as Bdim/G, or a Bdim triad over a G bass note. The diminished triad is made up of stacked minor 3rds, and the tension in the chord comes from there, specifically the imbedded tritone, but let’s not get too technical here.

Diminished 7th Chord
If you add one additional minor 3rd on top of the diminished triad, you get a diminished 7th chord (and more tension). In our example built on the G, that would be B D F Ab. With the bass note this is a Gb9 chord (the flat 9 being the same note as the flat 2, just up an octave). Don’t let the flat9 throw you, this is still just a dominant chord with a little embellishment. The magic of diminished 7th chords is that they are symmetrical, so a Bdim7 has the harmonic sound of a Ddim7, as does the Fdim7 and the Abdim7. That’s why we can move them 3 frets up or down the guitar neck and they sound similar. They are all inversions of each other, and names differ only based on the lowest note or context in which they are used. So in place of the G7 chord we have 4 choices for a diminished 7 chord built on the 3rd, 5th, flat 7th or flat 9th of the Dominant chord.

Conclusion and Take-away
Think of a diminished chord in a way similar to a dominant or secondary dominant. It is a tension chord resolving to a particular target chord. Which target? The same one as the dominant chord.

What chord are you resolving to? Find it’s Dominant or Secondary Dominant, and build your diminished chord on the 3rd, 5th, flat7th, or flat9th of that chord. The G7 resolves to C, and you can substitute the diminished chord built on the 3rd, 5th, flat7, or flat9 of the G chord.

This makes diminished chords and their use MUCH more accessible in my mind and opens up harmonic possibilities on the fretboard. If you know the dominant of the moment, using the CAGED shapes you find it’s chord tones very quickly. If you know the shape of the diminished 7 chord, almost on-the- fly, you can drop in a diminished chord or diminished arpeggio in place of that secondary dominant chord. With practice, this brings them well within reach.

[sunjamr]

Nice explanation, Michael. I learned it once, then forgot it, and now I’ve learned it again. I’ll probably forget it again after a while. Or maybe not.

Sunjamr Steve

[charjo]

Great review, Michael. Thanks for augmenting our understanding of diminished (see what I did there?).
John

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