A chord is three or more notes sounded together. Nearly all common chords are built by stacking thirds, which means skipping every other note of a scale.
One chord.
A few small distances.
Change a note. Hear a different feeling.
STACKED THIRDS4 + 3semitones
A major third, then a minor third. Listen for the settled sound. C is the bass. The selected keys show C, E, G.
Root position: the root is the lowest note.
Uppercase = major · lowercase = minor · ° = diminished
Start with C major, then choose Minor: only E moves, down one semitone to E♭. Try Major 7 to add B, then Dominant 7 to lower it to B♭. Use Note by note to hear each tone before hearing them together.
The distances in the display are measured from the root. The stacked-thirds formula counts the gaps between neighbouring chord tones in root position. Inverting a chord changes which note is lowest; it keeps the same chord tones and formula.
Intervals in semitones
An interval is the distance between two notes. Counting in half steps (semitones):
| Interval | Semitones |
|---|---|
| Minor 3rd | 3 |
| Major 3rd | 4 |
| Perfect 5th | 7 |
| Minor 7th | 10 |
| Major 7th | 11 |
Triads
A triad has three notes: a root, a third above it and a fifth above it. The sizes of the two stacked thirds decide the quality.
| Triad | Stack (semitones) | Example on C |
|---|---|---|
| Major | 4 + 3 | C E G |
| Minor | 3 + 4 | C E♭ G |
| Diminished | 3 + 3 | C E♭ G♭ |
| Augmented | 4 + 4 | C E G♯ |
Major sounds bright and settled, minor sounds darker, diminished sounds tense and unstable, and augmented sounds open and unresolved.
Seventh chords
Adding another third on top gives a seventh chord.
| Chord | Stack (semitones) | Example on C |
|---|---|---|
| Major 7 (maj7) | 4 + 3 + 4 | C E G B |
| Dominant 7 (7) | 4 + 3 + 3 | C E G B♭ |
| Minor 7 (m7) | 3 + 4 + 3 | C E♭ G B♭ |
| Half-diminished (m7♭5) | 3 + 3 + 4 | C E♭ G♭ B♭ |
The dominant 7 is the chord that naturally sits on the 5th degree of a major key and pulls strongly toward the tonic.
Diatonic chords
Build a triad on each note of a scale using only notes from that scale and you get the diatonic chords of the key. In C major:
| Degree | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| Chord | C | Dm | Em | F | G | Am | Bdim |
In A natural minor (the relative minor, same notes):
| Degree | i | ii° | III | iv | v | VI | VII |
|---|---|---|---|---|---|---|---|
| Chord | Am | Bdim | C | Dm | Em | F | G |
Notice the pattern in major: three major chords (I, IV, V), three minor (ii, iii, vi) and one diminished (vii°).
Roman numeral convention
Roman numerals name a chord by its position in the key rather than by absolute pitch, so the same progression can be moved to any key.
- Uppercase means a major chord: I, IV, V.
- Lowercase means a minor chord: ii, iii, vi.
- A ° after a lowercase numeral means diminished: vii°.
- Extensions are added after the numeral: V7, ii7, Imaj7.
In natural minor, the same rule gives i, iv and v as minor chords, and III, VI and VII as major.
Inversions and voicing
The notes of a chord can be reordered. If the third is the lowest note, the chord is in first inversion; if the fifth is lowest, second inversion. A seventh chord can also have its seventh in the bass: third inversion. The chord’s identity stays the same, but its bass and sound change. Choosing inversions can help successive chords connect with small movements.
Hear it yourself
Open the Scale & Mode Explorer, choose a key and play the chords built on each degree. Compare how the major, minor and diminished qualities feel in context.