Perfect, major & minor intervals

Every interval name has two words, like "perfect fifth" or "minor third." The first word is the quality; the second is the number. Once you know how to find each, you can name any interval on sight or by ear.

1. The number: counting letter names

The number tells you how many letter names the interval spans, counting both ends. From C up to G you pass C-D-E-F-G — five letters — so it's a fifth. From C to E is C-D-E, three letters, a third. Always count inclusively, starting with the lower note as "1." This part ignores sharps and flats entirely; it's pure letter-counting.

2. The quality: it depends on the number

Here's the key fact most explanations bury: not every interval number gets the same set of qualities. Intervals split into two families:

• The "perfect" family: unisons (1st), 4ths, 5ths, and octaves (8th). These are called perfect rather than major or minor.
• The "major/minor" family: 2nds, 3rds, 6ths, and 7ths. These come in major and minor versions.

So you'll never hear "major fifth" or "minor octave" — those numbers only take perfect. And you'll never hear "perfect third" — that number is major or minor.

3. Why are some intervals "perfect"?

The label is historical. Unisons, octaves, fourths, and fifths were considered the most consonant and stable — they blend so smoothly they sound almost "pure." Medieval theorists called them perfect to set them apart from the sweeter-but-richer thirds and sixths. The name stuck. A perfect interval doesn't have a major or minor form; it's simply perfect, or — if you shrink or stretch it by a half step — diminished or augmented.

4. Major vs. minor: just one half step

For the 2nds, 3rds, 6ths, and 7ths, the rule is simple: a minor interval is exactly one half step smaller than the major version. For example:

• Major 3rd = 4 half steps (C to E). Minor 3rd = 3 half steps (C to E♭).
• Major 6th = 9 half steps (C to A). Minor 6th = 8 half steps (C to A♭).

That single half step is the difference between a bright major sound and a darker minor one — the same contrast you hear between major and minor chords.

5. The fastest way to name any interval

Use the major scale of the lower note as your ruler:

1. Count the number by letters (inclusive).
2. Check if the top note is in the lower note's major scale.
3. If yes: it's major (for 2/3/6/7) or perfect (for 4/5/8).
4. If the top note is a half step lower than the scale tone: it becomes minor (or diminished for the perfect family).

Example: C up to A. Count: C-D-E-F-G-A = a 6th. A is in C major, so it's a major 6th. Lower it to A♭ and you get a minor 6th. Same method works from any starting note.

6. Quick reference

• Perfect: unison, 4th, 5th, octave — stable, open sound.
• Major / minor: 2nd, 3rd, 6th, 7th — minor is one half step smaller than major.
• Stretch a perfect or major interval by a half step → augmented.
• Shrink a perfect or minor interval by a half step → diminished.

Master perfect, major, and minor first; augmented and diminished are just the edges and will click once the core is solid.

Frequently asked questions

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