A chord is three or more notes played simultaneously to create harmony. Understanding chord construction — how chords are built from intervals — lets you figure out any chord by ear or analysis, and tells you what voicings and extensions will work in a given context. The chord symbol is a compact description of its construction; being able to decode and rebuild any symbol is a fundamental skill.
| Interval name | Abbreviation | Semitones | Example from C |
|---|---|---|---|
| Minor 2nd (half step) | m2 | 1 | C → D♭ |
| Major 2nd (whole step) | M2 | 2 | C → D |
| Minor 3rd | m3 | 3 | C → E♭ |
| Major 3rd | M3 | 4 | C → E |
| Perfect 4th | P4 | 5 | C → F |
| Tritone (aug 4th / dim 5th) | TT | 6 | C → F#/G♭ |
| Perfect 5th | P5 | 7 | C → G |
| Minor 6th (aug 5th) | m6 | 8 | C → A♭/G# |
| Major 6th | M6 | 9 | C → A |
| Minor 7th | m7 | 10 | C → B♭ |
| Major 7th | M7 | 11 | C → B |
| Octave | P8 | 12 | C → C |
Root, third, and fifth — the basic building block:
| Triad type | Construction | Semitones | Example (C) | Sound |
|---|---|---|---|---|
| Major | Root + M3 + P5 | 4 + 3 | C E G | Bright, resolved, stable |
| Minor | Root + m3 + P5 | 3 + 4 | C E♭ G | Darker, introspective, stable |
| Diminished | Root + m3 + d5 | 3 + 3 | C E♭ G♭ | Tense, unstable — wants to resolve |
| Augmented | Root + M3 + A5 | 4 + 4 | C E G# | Ambiguous, floating — symmetrical, no clear root |
| Suspended 4th | Root + P4 + P5 | 5 + 2 | C F G | Unresolved, ambiguous (no 3rd) |
| Suspended 2nd | Root + M2 + P5 | 2 + 5 | C D G | Open, floating (no 3rd) |
Add a fourth note (a seventh above the root) for the harmonic richness that jazz and modern harmony rely on:
| Chord type | Symbol | Construction | Example (C) | Typical function |
|---|---|---|---|---|
| Major 7th | maj7, Δ7 | M3 + P5 + M7 | C E G B | Tonic — stable, lush |
| Dominant 7th | 7 | M3 + P5 + m7 | C E G B♭ | Dominant — strong pull to resolution (tritone in 3rd and 7th) |
| Minor 7th | m7, −7 | m3 + P5 + m7 | C E♭ G B♭ | Pre-dominant (ii chord) or tonic (vi chord) |
| Minor-major 7th | m(maj7), mΔ7 | m3 + P5 + M7 | C E♭ G B | Tonic in minor key (Im with raised 7th) — exotic, unstable |
| Half-diminished | ø7, m7♭5 | m3 + d5 + m7 | C E♭ G♭ B♭ | ii° in minor key — pre-dominant |
| Diminished 7th | °7, dim7 | m3 + d5 + d7 | C E♭ G♭ B♭♭(A) | Diminished — symmetric, can resolve to any chord a half step above any note |
| Major 6th | 6, maj6 | M3 + P5 + M6 | C E G A | Tonic substitute in jazz (same notes as Am7 in root position) |
| Minor 6th | m6 | m3 + P5 + M6 | C E♭ G A | Minor tonic substitute |
Continue stacking thirds above the seventh to get 9ths, 11ths, and 13ths. These numbers refer to the same intervals as the 2nd, 4th, and 6th, raised by one octave:
9th = same pitch class as 2nd (M2 or m2 up an octave from root) 11th = same pitch class as 4th (P4 or #4 up an octave) 13th = same pitch class as 6th (M6 or m6 up an octave) Common extended chords: Cmaj9: C E G B D (maj7 + major 9th) C9: C E G B♭ D (dom7 + major 9th) Cm9: C E♭ G B♭ D (m7 + major 9th) C7#11: C E G B♭ F# (Lydian dominant — tritone against root) C13: C E G B♭ D A (dom7 + 9th + 13th — leave out 11th usually) Cmaj13: C E G B D F# A (all seven notes — rarely voiced complete)
In practice, extended chord voicings leave some notes out. The guiding principle is that the 3rd and 7th define the chord's identity:
| Note | Include? | Why |
|---|---|---|
| Root | Sometimes (often bass player's job) | Bass covers it — rootless voicings are common in jazz piano |
| 3rd | Always | Defines major vs minor quality |
| 5th | Often omit | Least interesting, adds little colour (unless altered) |
| 7th | Always (in jazz) | Defines dominant vs major vs minor character |
| 9th, 11th, 13th | Selective | Colour and context — choose what serves the melody and voice leading |
C major triad: Root position: C E G (root in bass) 1st inversion: E G C (3rd in bass) — written C/E 2nd inversion: G C E (5th in bass) — written C/G Seventh chord inversions: Cmaj7 root: C E G B Cmaj7 1st: E G B C (3rd in bass) — C/E Cmaj7 2nd: G B C E (5th in bass) — C/G Cmaj7 3rd: B C E G (7th in bass) — C/B
Inversions change the weight and stability. Second inversion (6/4 chord) sounds unstable over a non-root bass note — useful as a suspension before cadential resolution. Slash chords in pop (G/B, D/F#) specify the bass note of an inverted chord.
| Symbol | Meaning | Notes (from C) |
|---|---|---|
| C | C major triad | C E G |
| Cm | C minor triad | C E♭ G |
| C7 | C dominant 7th | C E G B♭ |
| Cmaj7 or CΔ | C major 7th | C E G B |
| Cm7 | C minor 7th | C E♭ G B♭ |
| C7sus4 | C dominant, suspended 4th | C F G B♭ |
| C7♭9 | C dominant, flat 9 | C E G B♭ D♭ |
| C7#9 | C dominant, sharp 9 ("Hendrix chord") | C E G B♭ D# |
| Cadd9 | C major triad + 9th (no 7th) | C D E G |
| C/E | C major in 1st inversion (E in bass) | E (bass) C E G |