A tetrachord (TC) is four successive tones separated by three intervals.

### The Names of Tetrachords

Tetrachords get described by the intervals between the tones.

Major: M2, M2, m2 → 221

Minor: M2, m2, M2 → 212

Upper Minor: m2, M2, M2 → 122

Whole Tone: M2, M2, M2 → 222

Harmonic: m2, m3, m2 → 131

Locrian: m2, M2, m2 → 121