What is the circle of fourths/fifths?
If we take the 12 notes of the chromatic scale and arrange each tone in a circle with its 4th and 5th intervals to either side of that tone, we will have a nice looking circle with some interesting properties. We can use this circle to compose melodies, harmonies, and modulations. This circle is known as the circle of fifths when the 5th interval is read clockwise and the circle of fourths when we reverse it to have the 4th intervals clockwise. We are going to be talking about jazz, so we're going to focus on the circle of fourths.
- Circle of Fourths/Fifths (e.g. iii - vi - ii - V - I)
Jazz is crazy about the ii V I progression. The extension of that: the iii vi ii V I.
Secondary dominant chords
- Folk/country music
Tritone substitution of V in II - V - I => e.g. Dm7 - Db7 - Cmaj7
- Tritone sub is as easy as looking to opposite note on circle
Augmented triads (major thirds)
Diminished 7th chords (minor thirds)
You may have noticed that the tone circle above has many additional tones joining the typical cycle. TODO.
- Change keys by intervals of Major 3rds (e.g. E -> C)
- 3 semitone = min 3rd (Minor Coltrane Changes – diminished 7th chord)
- 4 semitone = Maj 3rd (Coltrane Changes – augmented chord)
- 5 semitone = Perfect 4th (Standard Circle Progression)
- 6 semitone = Tritone (= two min 3rds)
- Giant Steps!
- Harmonic/Overtone series?
- Jazz! - resolve 5 -> 1 (creates a feeling of resolution) -> ii V I
- each note on the circle represents a key center
- the closer two keys are on the circle, the more notes they have in common
- key centers - most pop songs have a single key center
- Major Thirds (Giant Steps) and connected with V -> I