Diminished and augmented: the restless chords
Recognise the two chords that never sound settled, the squeezed diminished and the stretched augmented, and name all four triad types by their two gaps.
BEYOND MAJOR AND MINOR
Two chords that won't sit still
Major and minor chords can end a song. Their outer notes are a solid 7 half steps apart. Two other triads break that frame, and most listeners hear them as unsettled, as if the music is asking a question. Once you can spot them, film scores and suspense moments in songs start to make sense.
Play C–E♭–G, then C–E♭–G♭. The second one keeps the minor middle note but pulls the top note down. Most people hear it as tight and tense.
Diminished triad
Two minor thirds stacked: 3 + 3 half steps. The outer notes are only 6 half steps apart, one less than the usual 7. That squeezed gap, the tritone, is what gives the chord its tight sound. Written Bdim or B°.
B–D–F: B to D is 3, D to F is 3, B to F is 6. C–E♭–G♭: C to E♭ is 3, E♭ to G♭ is 3, C to G♭ is 6.
C minor and C diminished, counted in half steps from C.
note: C C♯ D E♭ E F G♭ G
half steps: 0 1 2 3 4 5 6 7
C minor: C E♭ G (0, 3, 7)
C dim: C E♭ G♭ (0, 3, 6)Same root, same middle note. Minor has its top note at 7; diminished pulls it down to 6.So a diminished chord starts like a minor chord and then squeezes. That is a handy way to picture it by ear.
Check yourself
Parisa plays C–E♭–G♭ and says 'it has E♭ in it, so it's C minor'. What is it really?
- C minor, because the middle note is E♭
- Not a real triad, because G♭ is a black key and triads use white keys
- C diminished: its outer gap is only 6
- C augmented, because it sounds unsettled
Show the answer
C diminished: its outer gap is only 6
Right. The minor third C–E♭ is there, but the top is G♭ (6), not G (7). Two minor thirds stacked, 3 + 3, make a diminished triad.
Augmented triad
Two major thirds stacked: 4 + 4 half steps. The outer notes are 8 half steps apart, one more than the usual 7. It starts like a major chord, then the top note is pushed up. Written C+ or Caug.
C–E–G♯: C to E is 4, E to G♯ is 4, C to G♯ is 8. Compare C major, C–E–G, where the top note sits at 7.
Two kinds of restless
Diminished · 3 + 3
Outer gap squeezed to 6. Most listeners describe it as tense, tight, anxious, like a spring pressed down. It usually sounds as if it wants to move to a nearby chord.
Augmented · 4 + 4
Outer gap stretched to 8. Most listeners describe it as stretched, floating, dreamy, like a question left hanging. It often shows up in film music for dreams or mystery.
Check yourself
- C–E–G: gaps 4 + 3, outer notes 7 apart. Most listeners hear it as settled.
- C–E–G♯: gaps 4 + 4, outer notes 8 apart. Most listeners hear it as stretched and unsettled.
Only one note changed between these two chords. What made the second one sound unsettled?
- The middle note moved, so it stopped being major
- The chord as a whole got higher, and higher chords always sound more tense
- The top note rose a half step, breaking the solid 7
- It has a black key in it
Show the answer
The top note rose a half step, breaking the solid 7
Exactly. The middle note E stayed put. Pushing G up to G♯ stretches the outer gap from 7 to 8, and that broken frame is what most ears hear as restless.
| Triad | Bottom gap | Top gap | Outer gap | From C |
|---|---|---|---|---|
| Major | 4 | 3 | 7 | C E G |
| Minor | 3 | 4 | 7 | C E♭ G |
| Diminished | 3 | 3 | 6 | C E♭ G♭ |
| Augmented | 4 | 4 | 8 | C E G♯ |
Check yourself
Count both gaps: diminished (3 + 3) or augmented (4 + 4)?
- B D F
- C E G♯
- D F A♭
- F A C♯
- E G B♭
- A♭ C E
Show the answer
Diminished: B D F, D F A♭, E G B♭
Augmented: C E G♯, F A C♯, A♭ C E
INSIDE C MAJOR
The one diminished chord on the white keys
Build a triad on each white key by playing one, skipping one, playing one. You get three major chords (C, F, G), three minor (Dm, Em, Am) and exactly one diminished: the one on B, B–D–F. No augmented triad appears at all on the white keys; you need a black key to build one.
B–D–F tends to lead somewhere: B likes to rise a half step to C, and F likes to fall a half step to E. Together they land on C–E, the heart of C major.
Check yourself
Match the two gaps to the triad type
Show the answer
- 4 + 3, outer gap 7 → Major
- 3 + 4, outer gap 7 → Minor
- 3 + 3, outer gap 6 → Diminished
- 4 + 4, outer gap 8 → Augmented
Check yourself
Tara hears a chord that clearly does not sound settled. She hums the root, then the middle note, and finds the small gap, 3 half steps, just like in a minor chord. What is her best answer?
- Minor, because the middle note is 3 above the root
- Augmented, because it sounds restless
- Diminished: small gap, restless sound
- Major, because a restless chord always has a bright, wide middle note
Show the answer
Diminished: small gap, restless sound
Yes. A 3-gap at the bottom rules out augmented (4 + 4), and the restless sound rules out minor. Diminished starts like minor and then squeezes the top.
Lesson recap
- Diminished = 3 + 3 (B–D–F, C–E♭–G♭), outer gap 6: most people hear it as tense and tight.
- Augmented = 4 + 4 (C–E–G♯), outer gap 8: most people hear it as stretched and dreamy.
- Major and minor keep a solid 7 on the outside and can sound settled; diminished and augmented break it.
- By ear: settled or restless first, then squeezed or stretched.
- On the white keys the only diminished triad is B–D–F, and there is no augmented one.