Music theory The basics
Chords and harmony
Triads, seventh chords, chord symbols, Roman numerals, inversions and the four main cadences explained simply.
Practise this on its own page: Chord progressions, Guitar chords.
Triads
A triad is a three-note chord built from stacked 3rds. The bottom note is the root, the middle note is the 3rd and the top note is the 5th.
There are four kinds of triad, depending on the size of the 3rd and 5th above the root.
| Quality | 3rd above root | 5th above root | Notes on C |
|---|---|---|---|
| Major | Major 3rd | Perfect 5th | C E G |
| Minor | Minor 3rd | Perfect 5th | C Eb G |
| Diminished | Minor 3rd | Diminished 5th | C Eb Gb |
| Augmented | Major 3rd | Augmented 5th | C E G# |
Seventh chords
A seventh chord adds one more 3rd on top of a triad, giving four notes. Its name comes from the triad underneath and the size of the 7th.
| Name | Triad plus 7th | Notes on C |
|---|---|---|
| Major seventh | Major triad + major 7th | C E G B |
| Dominant seventh (major-minor) | Major triad + minor 7th | C E G Bb |
| Minor seventh | Minor triad + minor 7th | C Eb G Bb |
| Half-diminished seventh | Diminished triad + minor 7th | C Eb Gb Bb |
| Diminished seventh | Diminished triad + diminished 7th | C Eb Gb Bbb |
Chord symbols
Chord symbols, used above songs and in pop and jazz, start with a capital letter for the root, plus a sharp or flat if needed. Signs after the letter show the quality.
On this site we write chords the way most song sheets do: C (C major), Cm (C minor), Cdim or C° (C diminished) and C+ (C augmented). Sevenths are C7 (dominant seventh), Cmaj7, Cm7, Cm7♭5 or Cø7 (half-diminished) and Cdim7 or C°7 (diminished). Other books use slightly different signs, such as Cmi or Cma7, so check the key in your music. Other books use slightly different abbreviations, so check the key in your music.
Roman numerals
Roman numerals name a chord by the scale step its root sits on. Capital numerals mean major chords, small numerals mean minor chords, a small circle means diminished and a plus sign means augmented.
In any major key the triads are I, ii, iii, IV, V, vi and vii°. Chords I, IV and V are built on the tonic, subdominant and dominant, and they are the three major chords in a major key.
| Numeral | Quality | Notes |
|---|---|---|
| I | Major | C E G |
| ii | Minor | D F A |
| iii | Minor | E G B |
| IV | Major | F A C |
| V | Major | G B D |
| vi | Minor | A C E |
| vii° | Diminished | B D F |
Inversions
The lowest note of a chord decides its inversion. If the root is lowest, the chord is in root position. If the 3rd is lowest, it is in first inversion, and if the 5th is lowest, it is in second inversion.
Seventh chords have one more: if the 7th is lowest, the chord is in third inversion. For example, a C major triad with E at the bottom is in first inversion.
Cadences
A cadence is the pair of chords at the end of a musical phrase. British and American books often use different names, so both are shown here.
- Watch out: American books also use 'imperfect authentic cadence' for a V to I cadence that is less strong, which is different from the British imperfect cadence.
| UK name | US name | Chords |
|---|---|---|
| Perfect | Authentic | V (or V7) to I |
| Imperfect | Half | Ends on V, coming from a chord such as I, ii, IV or vi |
| Plagal | Plagal | IV to I |
| Interrupted | Deceptive | V (or V7) to vi, usually |