Chord Theory: Diminished Chords

Next, we’ll continue our study of chord theory with an explanation of diminished chords. This article assumes that you’ve read the articles below, so read them if you haven’t already.

One Step at a Time
Intervals: your tape measure for music
Chord Theory: Triads
Chord Theory: Power Chords
Chord Theory: Major Chords
Chord Theory: Minor Chords

Are your eyes bleeding yet? No? Good, here’s to more read. Time to dissect the diminished chord. This chord lives up to its name because it is used much less often then major and minor chords. Although it is fun to think that the diminished chord’s name was chosen because of its popularity, the fact is that it is named after the diminished 5th interval in its structure.

A minor chord and a diminished chord have a very similar structure so we’ll use a B minor chord as a point of reference to study a B diminished chord. Using the recipe for a minor chord (minor third + major third) a B minor chord uses the notes B, D and F♯:

Notice that the B minor chord has a perfect fifth between its root and fifth. Okay, now that we’ve established the B minor chord, let’s see how a diminished chord is different. A diminished chord has a diminished fifth instead of a perfect fifth. Consequently, we have to flatten the fifth of a minor chord to create a diminished chord:

As you can see B diminished chord has the notes B, D and F. By flattening the fifth, we have shortened the distance between the third and the fifth of the triad. The recipe for a diminished chord is:

Root + minor third interval = Third
Third + minor third interval = Diminished (or flat) Fifth

I’ll use my knowledge of the fretboard to map out all of the Bs, Ds and Fs that I can easily reach with my fingers.

Diminished chords are highly dissonant and have a very unstable quality about them because of the presence of the diminished fifth. They are rarely used in pop music, but when they are used they usually act as a passing chord to quickly approach another, more consonant chord. They can also be used in a secondary dominant role, but often times it is better to use a dominant seventh chord instead.

Diminished chords truly are the red-headed step-child of musical harmony. Use that information to your advantage. If you want to add some unique, harmonic interest to your songwriting, use a diminished chord. It’ll get some attention.

Next: suspended chords.

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