Intervals — The Building Blocks
Major, minor, perfect — what the qualities mean
Why some intervals are "major/minor" and others are "perfect" — and the simple rule that decides which.
The qualities
There are five interval qualities:
- Perfect (P) — unison, 4th, 5th, octave. These sound stable and consonant. There’s no “major” or “minor” version — there’s only the perfect version.
- Major (M) — 2nd, 3rd, 6th, 7th in their “bright” form. These are the default in a major scale.
- Minor (m) — those same numbers (2nd, 3rd, 6th, 7th) but one half-step smaller. These are darker, mournful, mysterious.
- Augmented (A) — any interval raised one half-step from its perfect or major form. Often spelled with a ♯.
- Diminished (dim, °) — any interval lowered one half-step from its perfect or minor form. Often spelled with a ♭.
So a “minor 3rd” (3 half-steps) is one semitone smaller than a “major 3rd” (4 half-steps). Same letter count, different quality.
Why 4ths, 5ths, octaves are “perfect”
The perfect 4th, 5th, and octave have the simplest frequency ratios (4:3, 3:2, 2:1) and historically were considered the only “perfectly consonant” intervals. You don’t need to call them anything other than “perfect” — that’s just their name.
The cheat-sheet you’ll actually use
When someone says “play a third”, they almost always mean a major or minor third — context (the key/scale) decides which. Same with sixths and sevenths.
When someone says “play a fifth”, they almost always mean a perfect fifth. If they meant otherwise, they’d say “augmented” or “diminished”.
Recognising by sound
Listen to these well-known song openings (the first two notes of each):
| Interval | Famous melody opening |
|---|---|
| m2 | Jaws theme — that creeping half-step |
| M2 | “Happy Birthday” — first two notes |
| m3 | “Greensleeves” / Smoke on the Water riff (first two) |
| M3 | “When the Saints Go Marching In” — first two notes |
| P4 | “Here Comes the Bride” — first two notes |
| TT | “Maria” from West Side Story — “Ma-ri…” |
| P5 | Star Wars main theme — first two notes |
| m6 | “The Entertainer” — first two notes |
| M6 | NBC chimes — middle interval |
| m7 | Star Trek: TOS theme — first two notes |
| M7 | “Take On Me” chorus — that climbing note |
| P8 | “Somewhere Over the Rainbow” — first two notes |
Sing these out loud while you play them on the guitar. Within a week or two, your ear stops needing the reference song.