A three-chord song is a song whose music is built around three chords that are played in a certain sequence. A common type of three-chord song is the simple twelve-bar blues used in blues and rock and roll.
Typically, the three chords used are the chords on the tonic, subdominant, and dominant (scale degrees I, IV and V): in the key of C, these would be the C, F and G chords. Sometimes the V7 chord is used instead of V, for greater tension.
The I (tonic), IV (subdominant) and V (dominant) chords (primary triads) together encompass all seven tones of the tonic's major scale. These three chords are a simple means of covering many melodies without the use of passing notes.
The order of the chord progression may be varied; popular chord progression variations using the I, IV and V chords of a scale are:
- I – IV – V
- IV – I – V
- I – IV – I – V
- I – IV – V – IV
Beside the I, IV and V chord progression, other widely used 3-chord progressions are:[1]
- I – vi – V
- I – ii – V