Music Theory from ZeroMusic Theory
Chapter 31About 3 minAll chapters

Diminished chords and the tritone

A distance of six semitones — the tritone — is what refuses to settle. Diminished chords stack it, and get used as a passageway.

Chapter 8 waved Bdim away as "barely used". Time to collect on that. Once you know where the unsettled sound comes from, you can build tension and release deliberately.

Several chapters have said that G7 wants to move to C. Here is where that force comes from, connected back to the distances in chapter 26.

What is a dim (diminished) chord?

A chord stacked in minor thirds — three semitones at a time. Every gap is identical, so it never settles anywhere. On its own it sounds anxious; it earns its keep as a route into the next chord.

The tritone is where the pull comes from.

Six semitones — exactly half an octave

G7 contains B and F. Those two are six semitones apart, which is precisely half of an octave (12). Being dead centre, it is the same distance in either direction, so nothing decides where it should go. That is the unsettled sound.

B and F. Just those two notes already refuse to settle.Buttons and keys in the diagrams play sound. Check your volume first.

That pair is why G7 pulls to C. B wants to rise a semitone to C, and F wants to fall a semitone to E. The chord where both land at once is C — which is why G7 → C is so satisfying.

In plain wordsTritone

A distance of six semitones. Exactly half an octave, equidistant in both directions, so it never settles. The tension in seventh chords comes from here.

Diminished chords are stacked minor thirds

A diminished chord stacks minor thirds — three semitones each. Stack four notes and every pair is either a minor third or a tritone: perfectly even. It is unsettledness taken to its extreme.

  • BdimBdim (three notes)
  • Bdim7Bdim7 (four notes, perfectly even)
  • CC (resolution)
Three notes, then four, then C. Listen to the release when the settled chord arrives.Buttons and keys in the diagrams play sound. Check your volume first.

The third one lands hard. A diminished chord is unstable alone, but put a stable chord after it and the contrast becomes the effect.

What it is actually for

  • As a passageway — C → C♯dim → Dm, sitting between chords so the bass walks up by semitone.
  • To build tension — before a chorus or a key change, making the listener wait.
  • As a substitute — in place of a seventh chord, keeping a similar pull with a different colour.
  • Straight (C, Dm, G, C)

    C | Dm | G | C

  • With a passing chord (C, C♯dim, Dm, G)

    C | C#dim | Dm | G

The second version puts C♯dim between C and Dm, so the bass walks C → C♯ → D.Buttons and keys in the diagrams play sound. Check your volume first.

The second one connects more smoothly for the same progression. Like the inversions in chapter 11, this is a tool for tidying up what the bass does.

Generate over a progression containing a passing diminished chord and hear how the melody crosses a bass that moves by semitone.

Generate over C, C♯dim, Dm, G
The one thing to remember

The tritone is where the pull comes from. Diminished chords put that pull to work as a passing chord.

Quick review

Everything here is answerable from this chapter. Pick an option and the answer appears straight away.

  1. Question 1

    How many semitones is a tritone?

  2. Question 2

    What is the most common use of a diminished chord?