Intervals

An interval is the distance between two notes. Every scale and every chord is built from intervals, so once you can name them, the rest of music theory gets much easier.

Naming an interval

An interval has two parts: a number and a quality. In major 3rd, “3rd” is the number and “major” is the quality.

  1. The number: count the letter names. Count both notes and every letter in between. C to E is C, D, E: three letters, so it is a 3rd. C to G is C, D, E, F, G: a 5th.
  2. The quality: count the semitones. A semitone is the step from one key to the very next, black or white. C to E is 4 semitones, which makes it a major 3rd. C to E♭ is 3, a minor 3rd.

The letters decide the name, not just the keys. C to F♯ and C to G♭ are the same two keys, 6 semitones apart, but C to F♯ uses four letters (an augmented 4th) and C to G♭ uses five (a diminished 5th).

Every interval from C

Measured up from C, with both notes marked on the keyboard.

Intervals in scales

Measured from the first note, every note of a major scale is a major or perfect interval: M2, M3, P4, P5, M6, M7 and the octave. See it in the C major scale.

The natural minor scale lowers the 3rd, 6th and 7th: M2, m3, P4, P5, m6, m7 and the octave. Compare the C minor scale.

Between neighbouring notes, scales move in 2nds: a tone (major 2nd, a whole step) or a semitone (minor 2nd, a half step).

Intervals in chords

Triads are two 3rds stacked on top of each other. A major triad is a major 3rd with a minor 3rd above it (C–E–G). A minor triad swaps them: a minor 3rd, then a major 3rd (C–E♭–G). Either way, root to top is a perfect 5th.

Turning an interval upside down

Move the lower note up an octave and you get the interval’s inversion. C to E (a major 3rd) becomes E to C (a minor 6th).