Diatonic 2, 3, 6, 7
Section outline
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The quality of seconds, thirds, sixths and sevenths is major or minor.
Seconds

Thirds


Sixths and sevenths
If interval includes one minor second, it's major sixth/seventh.. If it includes two minor seconds, it's minor sixth/seventh.

Sixth compared to fifth:
- Major sixth is fifth + M2 (major scale, C-A)
- Minor sixth is fifth +m2 (minor scale, C-Ab)
Seventh compared to octave:
- Major seventh is m2 less than octave
- Minor seventh is M2 less than octave