Harmony and cadences
Chords in a key
Build a triad on each note of a major scale. In C major:
| I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|
| C | Dm | Em | F | G | Am | Bdim |
Capitals are major, lowercase minor, ° diminished. The most important chords are I (tonic), IV (subdominant) and V (dominant). In C major those are C, F, G. In A major: A, D, E.
Cadences
A cadence is a harmonic ending.
- Authentic: V → I (strong finish)
- Plagal: IV → I ("amen")
- Half: ends on V (feels unfinished)
- Deceptive: V → vi (surprise)
Leading tone
The 7th degree, a semitone below the tonic, wants to resolve upward. In harmonic minor it makes the V chord major.
Beyond the key
- A secondary dominant such as V/V (D7 in C major) briefly points to another chord.
- A tritone substitution swaps G7 for D♭7; both contain the same tritone.
- Modulation is a full change of key.