Interval quality: major, minor, perfect…
Music theory · Intervals · Level 3 · 14 min
C-E and C-E♭ are both thirds (three letter names), yet they don't sound the same: the first is bright, the second darker. The number is not enough; you need the quality, which depends on the exact number of half steps.
The qualities
- Seconds, thirds, sixths and sevenths can be major (M) or minor (m, one half step smaller).
- Unisons, fourths, fifths and octaves are perfect (P) in their normal form.
- Any interval can be augmented (one half step larger than major or perfect) or diminished (one half step smaller than minor or perfect).
| Half steps | Interval | From C |
|---|---|---|
| 0 | perfect unison (P1) | C |
| 1 | minor 2nd (m2) | D♭ |
| 2 | major 2nd (M2) | D |
| 3 | minor 3rd (m3) | E♭ |
| 4 | major 3rd (M3) | E |
| 5 | perfect 4th (P4) | F |
| 6 | augmented 4th (A4) / diminished 5th (d5) — the tritone | F♯ / G♭ |
| 7 | perfect 5th (P5) | G |
| 8 | minor 6th (m6) | A♭ |
| 9 | major 6th (M6) | A |
| 10 | minor 7th (m7) | B♭ |
| 11 | major 7th (M7) | B |
| 12 | perfect octave (P8) | C |
M:4/4 L:1/4 Q:1/4=72 K:C "^m2"[C_D]2 "^M2"[CD]2 | "^m3"[C_E]2 "^M3"[CE]2 | "^P4"[CF]2 "^d5"[C_G]2 | "^P5"[CG]2 "^m6"[C_A]2 | "^M6"[CA]2 "^m7"[C_B]2 | "^M7"[CB]2 "^P8"[Cc]2 |]
A two-step method
- The number: count letter names, ignoring accidentals (D-F♯ → D, E, F → a third).
- The quality: count half steps (D → F♯ = 4) and compare with the table → major third.
The quick major-scale method: imagine the major scale of the lower note. If the upper note belongs to it, the interval is major (2, 3, 6, 7) or perfect (1, 4, 5, 8). One half step below that scale note → minor (or diminished for a perfect interval). Example: A-F. A major scale: A B C♯ D E F♯… F is a half step below F♯ → minor sixth.
Worked examples
- E – G: a third; 3 half steps → minor third.
- F – B: a fourth; 6 half steps → augmented fourth (tritone). It is the only fourth between white keys that isn't perfect.
- B – F: a fifth; 6 half steps → diminished fifth.
- C – D♯: a second; 3 half steps → augmented second (which sounds like a minor third!).
- C♯ – E♭: a third; 2 half steps → diminished third.
Never name by ear alone: C-D♯ and C-E♭ sound identical on the piano, but one is an augmented second and the other a minor third. The number always comes from the spelling.
Learn by heart: major third = 4 half steps, minor third = 3, perfect fifth = 7. With these three numbers you can build every chord in the next part of the course.
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