What is a Diminished Triad?

Diminished Triad

Most time I prefer to relate the diminished triad with our regular minor triads because it’s just only one note (the last note) that differentiate it from the minor triad. That note is called the diminished fifth (reduced fifth).

The diminished triad is made up of 3 notes having intervals of a minor third (1 and half semitone) between them each.

The diminished triad formula is written below:

Root + minor 3rd + diminished 5th = Diminished triad

We can easily spot the slight difference when compared with the minor chord formula

Root + minor 3rd + Perfect 5th = minor chord

The diminished triad is built on the 7th degree of the major scale and this technically means that it’s going to be the “7 chord” (NOT 7th Chord). It is a lonely chord unlike the major and minor chords group that has 3 chord members each. However the 7 chord (diminished triad) provides a vivid connection to either the 1 chord or the 3 chord which means in a song you might want to play the 7 chord quickly before the 1 chord or 3 chord.

Let’s examine the diminished triad in the key of C major.

Since we build our diminished chord on the 7th degree of the scale, hence we are taking the B as the root of the diminished chord in key C major since B is the 7th note on the C major scale.

This implies that we are actually looking for a B diminished triad to represent the 7 chord in the key of C major.

Like I said before earlier, I relate the diminished triad with our regular minor triads hence we would take the root “B” and play a “B natural minor scale” first

Here is the diminished triad formula one more time

Root + minor 3rd + diminished 5th = Diminished triad

The root is B

The minor 3rd is D (1 and half tone away from root B)

The diminished 5th is F (3 tones away from the root B; F# being the perfect 5th is flattened by a semitone to give the diminished 5th F)

In summary, the “7 chord” (NOT 7th chord) in the key of C is;

B diminished triad = BDF

 

Conclusively, the rule of thumb for getting our diminished triad:

  1. Identify the key you are in and write out the Major scale of that key.
  2. Secondly, recognize the note on the 7th scale degree (in key C it’s the note B).
  3. Pick that note and spell out the natural minor scale starting from that note; if “B” is the 7 then write out the B natural minor scale since you are looking for the “7 chord” which is B diminished triad.
  4. Finally use the diminished triad formula “Root + minor 3rd + diminished 5th = Diminished triad” to identify each note of that particular diminished triad you are looking for.
  5. Repeat same steps for every diminished triad you are looking for in that key you are in.

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