Music Theory · Harmony
How the circle of fifths works, what relative keys are, how diatonic chords are built, and why neighboring keys sound so good together.
Fundamentals
The circle of fifths arranges all 12 keys in a circle, each separated by a perfect fifth (7 semitones). Moving clockwise, the key rises by a fifth — and each new key gets exactly one more sharp in its scale. Counter-clockwise, the key falls by a fifth, each key gaining one more flat.
Adjacent keys in the circle of fifths share 6 of 7 notes — that's why modulations between them sound so natural and smooth. A jump from C major to G major feels more familiar than to F♯ major, because C and G are only one fifth apart.
Every major key has a relative minor key with identical key signature. The minor key starts 3 semitones below the major key.
| Major Key | Key Signature | Relative Minor |
|---|---|---|
| C major | none | A minor |
| G major | 1 sharp (F♯) | E minor |
| D major | 2 sharps | B minor |
| A major | 3 sharps | F♯ minor |
| E major | 4 sharps | C♯ minor |
| F major | 1 flat (B♭) | D minor |
| B♭ major | 2 flats | G minor |
| E♭ major | 3 flats | C minor |
| A♭ major | 4 flats | F minor |
Every key has 7 natural chords — one on each scale degree. Three of them are particularly important:
The cadence I → IV → V → I (e.g. C → F → G → C) is the backbone of blues, rock, pop and country. It works the same way in every key.
| Degree | Chord | Type | Function | Mode |
|---|---|---|---|---|
| I | C | Major | Tonic | Ionian |
| II | Dm | Minor | Supertonic | Dorian |
| III | Em | Minor | Mediant | Phrygian |
| IV | F | Major | Subdominant | Lydian |
| V | G | Major | Dominant | Mixolydian |
| VI | Am | Minor | Submediant | Aeolian |
| VII | Bdim | diminished | Leading tone | Locrian |