Tetrachords
A four-note scale segment (degrees 1–4 or 5–8). Every diatonic scale is two stacked tetrachords.
The Idea
Splitting a scale into lower (1–4) and upper (5–8) tetrachords reveals how modes relate. Swapping tetrachords shifts modal color without losing the tonal center.
| Tetrachord | Formula | Notes from C |
|---|---|---|
| Major (Ionian) | R–W–W–H | C D E F |
| Minor (Dorian) | R–W–H–W | C D E♭ F |
| Upper Minor (Phrygian) | R–H–W–W | C D♭ E♭ F |
| Whole Tone (Lydian) | R–W–W–W♯ | C D E F♯ |
- Moving in 5ths: swaps upper tetrachord, sharpens the 7th of the next upper tetrachord
- Moving in 4ths: swaps lower tetrachord, flattens the 4th of the next lower tetrachord
Chord families (C Major):
| Family | Chords | Tetrachords |
|---|---|---|
| Tonic | I, vi | Major, Minor |
| Predominant | ii, IV | Minor, Phrygian |
| Dominant | V, vii° | Mixolydian, Lydian |
On the Fretboard
N Notes per String
- Full tetrachord on a single string
- 3 notes on upper string, 1 note on lower string
- 2 notes each string
- 1 note on upper string, 3 notes on lower string
Exercises
- Play each tetrachord shape on a single string, then across two strings
- Create Modes by swapping tetrachords
- In a ii–V–I, swap only the upper tetrachord on the V chord for color
- Target guide tones (3rd and 7th) within each tetrachord