Augmented and Diminished Chords Explained

Play a B diminished triad and you hear something unsettled — three notes that want to move somewhere else. Add a fourth note to make a diminished seventh and that restlessness multiplies: now four notes are pulling in four different directions at once. Play an augmented triad and you get a third kind of tension, a floating, suspended quality. These chords are built from two special interval recipes, and once you understand the construction, the sound makes immediate sense.

This article covers the diminished triad, the diminished seventh, the half-diminished seventh, and the augmented triad — what they are made of, why they sound the way they do, where they appear in keys, and how they resolve. These four chord types sit alongside major and minor triads in the full picture of chord quality; this article goes deeper on these specific qualities and shows them across multiple roots.

The diminished triad

A triad is two stacked thirds. The diminished triad stacks two minor thirds: root to the 3rd is 3 half steps, and the 3rd to the 5th is another 3 half steps, putting the fifth at 6 half steps from the root.

That outer interval — 6 half steps — is the tritone. It is the defining sound of the diminished triad: the 5th is a diminished (narrowed) 5th above the root, not the perfect 5th (7 half steps) of a major or minor triad. The tritone is the most harmonically unstable interval in tonal music — two notes pulling in opposite directions, each wanting to resolve to a neighbor a half step away.

B diminished (B°): B–D–F. B to D = 3 half steps (minor 3rd), D to F = 3 half steps, B to F = 6 half steps (tritone). C diminished (C°): C–E♭–G♭. C to E♭ = 3 half steps, E♭ to G♭ = 3 half steps. D diminished (D°): D–F–A♭. D to F = 3 half steps, F to A♭ = 3 half steps. The recipe is the same from any root: the 3rd is a minor third above the root, the 5th is a minor third above the 3rd.

B°, C°, D° and E° with their note names. The pattern 3 + 3 half steps applies to every root; the 5th is always a tritone (6 half steps) from the root.

The diminished triad worksheet builds the chord in all twelve keys.

B° and C° on the keyboard. Count each key — black or white — from one chord tone to the next: the 3 + 3 pattern means every note in the triad lands three keys after the previous one.

Where the diminished triad appears

In a major key, the diminished triad appears on the seventh degree (vii°). In C major, the seventh degree is B, and B–D–F is the only diminished triad built from the white keys of C major. In a natural minor key, the diminished triad appears on the second degree (ii°). In A minor, the second degree is B, and B–D–F plays the role of the unstable chord leading toward the dominant.

The diminished triad's tritone makes it want to resolve. In C major, B° (vii°) most often moves to I: B rises a semitone to C, D holds or falls, and F falls a semitone to E. The outer voices contract inward, exactly as the tritone always does.

B° resolving to C major: B rises a semitone to C, F falls a semitone to E. The tritone contracts inward — the same motion that drives the dominant cadence.

For a broader picture of how chords relate to their scale degrees and Roman numeral labels, the scale degrees worksheet is a good companion.

The diminished seventh chord

Add one more minor third on top of the diminished triad and you get the diminished seventh chord (°7). The structure is four notes with 3 half steps between every adjacent pair.

B diminished seventh (B°7): B–D–F–A♭. B to D = 3 half steps, D to F = 3 half steps, F to A♭ = 3 half steps, B up to A♭ = 9 half steps (a diminished 7th). Note that the 7th is spelled A♭, not G♯: A♭ is a 7th above B by letter count (B–C–D–E–F–G–A spans seven letter names), and lowering A by a semitone gives A♭. G♯ sounds identical on the piano but would be an augmented 6th, which does not describe a seventh chord. C diminished seventh (C°7): C–E♭–G♭–B♭♭. G♭ to B♭♭ = 3 half steps (B♭♭ is enharmonically A). E diminished seventh (E°7): E–G–B♭–D♭. Each step is 3 half steps.

Five diminished seventh chords from B to F. Every chord has 3 half steps between adjacent notes and contains two tritones: one between the root and the 5th, and one between the 3rd and the 7th.

The diminished seventh worksheet covers the chord in all keys.

The symmetry of the diminished seventh

The diminished seventh chord is the most symmetrical chord in tonal music. Because every note is 3 half steps from its neighbor, the four notes divide the octave into four equal parts. All four inversions of any diminished seventh chord are rotations of the same shape, which means only three distinct diminished seventh chords exist in equal temperament. What looks like four different chords — B°7, D°7, F°7, and A♭°7 — are four names for exactly the same set of keys: B, D, F and A♭. Treat D as the root and you have D°7; treat F as the root and you have F°7.

This symmetry is what gives the diminished seventh chord its remarkable harmonic flexibility: it can function as a leading-tone chord in four different keys. B°7 can resolve convincingly to C major/minor, E♭ major/minor, G♭ major/minor, or A major/minor. Romantic composers — Beethoven, Schubert, Chopin — exploited this constantly to pivot between remote keys without obvious preparation.

Only three distinct diminished seventh chords exist. Each group shares the same set of pitch classes; the four names in each group are the enharmonic inversions of one chord.

The standard resolution of B°7 to C major contracts all four voices inward by a semitone: B rises to C, D falls to C (or holds), F falls to E, A♭ falls to G. That simultaneous inward pull produces the dramatic, urgent arrival that makes diminished sevenths so effective before climactic moments in classical and film music. For the diminished seventh arpeggios that appear so often in Baroque and Classical period writing, the diminished seventh arpeggios worksheet is a good practical companion.

The half-diminished seventh (m7♭5)

The half-diminished seventh uses a diminished triad but adds a minor 7th on top — not the diminished 7th of the full °7 chord. That single note change transforms both the sound and the harmonic function.

B half-diminished (Bø7, also written Bm7♭5): B–D–F–A. The triad B–D–F is the same diminished triad (3 + 3 half steps). F up to A = 4 half steps (a major third), making the interval from root to 7th a minor 7th (10 half steps) rather than the 9-half-step diminished 7th of B°7. C half-diminished (Cø7): C–E♭–G♭–B♭. C–E♭ = 3, E♭–G♭ = 3, G♭–B♭ = 4, C to B♭ = 10 half steps. E half-diminished (Eø7): E–G–B♭–D. E–G = 3, G–B♭ = 3, B♭–D = 4 half steps.

Compare B°7 and Bø7 side by side: B°7 = B–D–F–A♭ (diminished 7th above B: 9 half steps); Bø7 = B–D–F–A (minor 7th above B: 10 half steps). One note — one half step — separates them, but the character shifts noticeably: the half-diminished has a softer, more melancholic color where the full diminished seventh feels urgent and tonally ambiguous.

B°7 and Bø7 side by side. The 5th is F in both; only the 7th changes — from A♭ (9 half steps above B) to A natural (10 half steps). One semitone makes a large difference to how the chord resolves.

The half-diminished seventh worksheet covers the chord in context.

The half-diminished seventh's natural home is the ii° chord in a minor key (iiø7). In A minor, the ii chord is B–D–F–A: Bø7. It resolves to the dominant E7 and from there to the tonic, giving the iiø7–V7–i progression central to jazz and minor-key classical writing. In D minor: Eø7–A7–Dm. In a major key, the equivalent of iiø7 sits on the vii of the key but is usually replaced by a full dominant seventh chord on V; the half-diminished appears far more often as the ii of minor. Jazz musicians hear it plainly as the natural "minor two chord" in every minor ii–V–i progression, and once you can recognize Bø7 and its relatives by sound, you will hear it throughout jazz standards and classical chamber music alike.

The augmented triad

Where the diminished triad stacks two minor thirds, the augmented triad stacks two major thirds. Root to 3rd is 4 half steps; 3rd to 5th is another 4 half steps; root to 5th is 8 half steps (an augmented fifth, one semitone wider than a perfect fifth).

C augmented (C+): C–E–G♯. C to E = 4 half steps, E to G♯ = 4 half steps, C to G♯ = 8 half steps. D♭ augmented (D♭+): D♭–F–A. D♭ to F = 4, F to A = 4. D augmented (D+): D–F♯–A♯. D to F♯ = 4, F♯ to A♯ = 4. E♭ augmented (E♭+): E♭–G–B. E♭ to G = 4, G to B = 4 (B is the correct spelling — not C♭, because C would be a 6th above E♭ by letter count, and we need a 5th). Our augmented triad worksheet covers correct spelling across roots.

C+ (C–E–G♯), D♭+ (D♭–F–A), D+ (D–F♯–A♯) and E♭+ (E♭–G–B) — one chord from each of the four distinct augmented triad families. The 4 + 4 half-step pattern applies from every root.

C+ and G+ on the keyboard. The 4 + 4 pattern means each chord tone lands four keys after the previous one, always skipping three keys to get to the next chord tone.

The symmetry of the augmented triad

Just as the diminished seventh divides the octave into four equal parts, the augmented triad divides the octave into three equal parts of 4 half steps each. This means only four distinct augmented triads exist in equal temperament. C+, E+ and A♭+ are three names for the same set of pitch classes (C, E, G♯/A♭). Similarly, D♭+, F+ and A+ share D♭, F, A. The four distinct sets are: {C, E, G♯}, {D♭, F, A}, {D, F♯, A♯}, and {E♭, G, B}.

The augmented triad is also a subset of the whole-tone scale (C–D–E–F♯–G♯–A♯): the triad C–E–G♯ uses three alternating steps from that scale. This connection gives both the triad and the scale their floating, directionless quality.

Only four distinct augmented triads exist in equal temperament. Each group shares the same three pitch classes; the three names are the three enharmonic inversions of one chord.

Where the augmented triad appears

As III+ in harmonic minor: The augmented triad's most natural home in common-practice music is the third degree of the harmonic minor scale. In C minor (harmonic: C–D–E♭–F–G–A♭–B), the third degree is E♭, and a triad built on E♭ using scale tones is E♭–G–B — that is E♭ augmented. The augmented triad is a by-product of raising the 7th degree in harmonic minor; the B pushes the triad built on the 3rd into augmented territory.

As V+ (augmented dominant): Perhaps the most dramatic use. The dominant triad in C major is G–B–D. Raise the 5th by a semitone to D♯ and you get G+ (G–B–D♯). D♯ wants to rise to E (the 3rd of the tonic chord), while B still wants to rise to C. The augmented 5th pushes upward with particular force, giving V+ a double upward tendency toward I. Composers from Wagner and Liszt to Debussy used V+ frequently for its strong chromatic dominant function.

As a chromatic passing chord: The augmented triad's smooth voice-leading also makes it useful as a chromatic passing harmony between two more stable chords. For example, moving from C major to Am can pass through C+: C–E–G becomes C–E–G♯ becomes C–E–A (Am). The G♯ is a chromatic passing tone in the inner voice. This kind of chromatic glide — one inner voice rising by a half step while the other voices hold — became a signature sound of late-Romantic and early Impressionist piano writing.

Comparing and resolving all four

Each chord has a characteristic sound and resolution path.

Diminished triad: Tense and unstable, with the characteristic tritone between the outer notes. It almost always resolves to a chord a half step above the root or a third above, with the tritone contracting inward.

Diminished seventh: More complex instability — four notes pulling inward simultaneously. Because it can resolve to four keys equally well, it is the pivot chord of Romantic music. All four voices resolve inward by a semitone toward the nearest tonic chord tone.

Half-diminished seventh: Softer and more melancholic than the full diminished seventh. The minor 7th on top takes the sharp edge off. Jazz musicians hear it as the natural ii chord in minor; in a iiø7–V7–i context the chord resolves by step toward the dominant.

Augmented triad: Floating and suspended, with no note feeling more like the root than the others. When it resolves as V+ to I, the augmented 5th rises by semitone (D♯ → E) and the leading tone rises as usual (B → C), creating a strong double upward pull.

Three standard resolutions. B°7 to C: all four voices contract inward by a semitone. Bø7–E7–Am: the classic iiø7–V7–i in A minor. G+ to C: D♯ rises to E while B rises to C.

The four chord types on C. The diminished triad and both seventh chords share the C–E♭–G♭ triad; the augmented triad raises the 3rd and uses a completely different 5th.

Chord symbols at a glance

A quick guide to spotting these chords in lead sheets and chord charts:

• B° or Bdim: B diminished triad (B–D–F)
• B°7 or Bdim7: B diminished seventh (B–D–F–A♭)
• Bø7 or Bm7♭5: B half-diminished seventh (B–D–F–A)
• C+ or Caug: C augmented triad (C–E–G♯)

The ° and ø symbols appear in classical and jazz notation; lead sheets often prefer dim and m7♭5 (spoken "minor seven flat five"). The augmented + sign is universal, though Caug appears in some older charts. For the full chord symbol system, the chord symbols chart worksheet covers every common suffix with examples on C.

Quick-reference: symbols, spellings, interval recipes and contexts for the diminished triad, diminished seventh, half-diminished seventh and augmented triad.

Practice suggestions

The best way to internalize these chords is to compare them directly on the keyboard in the same key.

Stack them on C: Play C°, then C°7, then Cø7 and C+ in sequence. Notice the single-note change between C°7 and Cø7 — only the 7th changes (B♭♭ to B♭), but the character shifts. Then compare C° with C+: same root, completely different quality because one raises the 5th and one lowers it.

Resolve each one: After playing B°7, resolve it to C major and notice the inward pull in all four voices. After playing G+, resolve it to C and notice the upward push of the augmented 5th. The directionality of each chord is different, and hearing that difference is the goal.

Transpose across four roots: Work through the diminished seventh worksheet and the augmented triad worksheet in several keys. Because only three distinct diminished seventh chords and four distinct augmented triads exist, many fingerings repeat, and you will start to notice the symmetry physically under your hands.

Use them in short progressions: In C major, try vii°–I (B°–C), vii°7–I (B°7–C), and V+–I (G+–C). In A minor, try iiø7–V7–i (Bø7–E7–Am). These short progressions are the clearest way to hear the resolution function of each chord. Once you can play each one fluently, start noticing them in music you already know — a diminished seventh chord before a dramatic arrival, an augmented dominant at the peak of a phrase. The dominant seventh worksheet and cadences worksheets show the dominant function in full harmonic context, and the chords of a minor key worksheet puts iiø7, V7 and i together in a minor key setting.

Sources

• Diminished triad — Wikipedia
• Diminished seventh chord — Wikipedia
• Half-diminished seventh chord — Wikipedia
• Augmented triad — Wikipedia
• Harmonic minor scale — Wikipedia
• [Stefan Kostka and Dorothy Payne, Tonal Harmony (8th ed., 2018), chapters 5–6]
• [Mark Levine, The Jazz Theory Book (1995), chapter 1 — chord qualities]