One-Octave Diminished Triad

What is the Diminished Triad?

The diminished triad is one of the four basic triads commonly used in music. It is the third most common triad you’ll encounter after the major triad and minor triad.

In music we use the term diminish to mean make smaller or lower. The diminished triad has a “diminished 5th” meaning it has a flatted, or lowered, 5th (in comparison to the typical perfect 5th found in most chords like the major and minor triads). The flat fifth is what gives the diminished triad its name and plays an essential part in its sound.

The easiest way to think of a diminished triad is to think of it as a minor triad with a flatted fifth.

The diminished triad is a very tense and unstable sounding chord. As a result, it doesn’t get used anywhere near as much as the major and minor triads or the major, minor and dominant 7th chords.

You will most encounter this triad in gospel, jazz, blues, some rock tunes, and Classical music. You will hear it on songs with more complex chord progressions or prettier chord progressions. Using this chord is mysterious to a lot of people and unfortunately its use gets over-looked in a lot of modern-day chord progressions.

Though it’s less common, the diminished triad is still essential to learn and understand. Don't ignore it.

Thirds Construction of the Diminished Triad

In terms of thirds construction, the diminished triad is built entirely of minor thirds:

Root to 3rd = m3
3rd to 5th = m3

Intervallic Construction of the Diminished Triad

The intervals for the diminished triad are: Root, m3, and D5.

Diminished Triad Fingering

A simple fingering for the diminished triad starts on your first finger. Play:

Root – 1st finger
Flat 3rd – 4th finger
Flat 5th – 2nd finger
Octave – 3rd finger

Diminished Triad Notation

The diminished triad has two common ways of being notated. The best and most readable one is the suffix “dim”. A diminished triad with a C root note would be notated Cdim.

Another common way is with a degree symbol (o). A diminished triad with a C root note could also be notated Co. This can be harder to read on charts and you should avoid writing it this way if you can. But, you should recognize it if someone else writes it that way.

Applying the Diminished Triad

Because of its unstable sound, the diminished triad is rarely played for a long stretch of time. Instead, it is used more often as a transition chord leading to some other chord.

Within chord progressions this chord often creates chromatic connections between a pair of chords. Many times an interesting chromatic root note line results from these types of progressions. For example, the chord progression C – C#dim – Dm would create a chromatic root movement of C to C# to D.

For bass players it’s particularly important to not play the wrong 5th on a diminished triad. Since bassists are used to stressing the roots and fifths of chords so much, it’s a common mistake to play a perfect fifth rather than a diminished 5th. Hitting the wrong 5th on this chord will ruin the sound and function of this chord most times.

Diminished Triad Example Usage

Here is an example of using the diminished triad.

Diminished Triad Details
Thirds construction: m3, m3
Intervallic construction: Root, m3, D5, (P8)
C diminished triad spelling: C, Eb, Gb

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