II Intervals & scales · Chapter 1
Intervals: the distance between two notes
Counting semitones, naming the gaps — the unit that scales and chords are built from.
Part I gave us twelve notes. Part II is about what happens between them.
An interval is the distance between two notes. That’s the whole concept. Everything else in this chapter — the names, the quality system, the abbreviations — is just vocabulary for talking about distances precisely.
Counting in half steps
The most honest way to measure an interval is to count how many half steps separate the two notes. From C Do to the next C Do is 12 half steps (a full octave). From C Do to D Re is 2 half steps. From C Do to E Mi is 4. Count the keys on a keyboard, including the black ones, and you have the answer.
Intervals have names
Counting works, but musicians invented names so they could talk about the quality of an interval without doing math every time. The names look intimidating at first — major third, perfect fifth, minor seventh — but they follow a pattern.
| Half steps | Name | Short |
|---|---|---|
| 0 | Perfect unison | P1 |
| 1 | Minor second | m2 |
| 2 | Major second | M2 |
| 3 | Minor third | m3 |
| 4 | Major third | M3 |
| 5 | Perfect fourth | P4 |
| 6 | Tritone | TT |
| 7 | Perfect fifth | P5 |
| 8 | Minor sixth | m6 |
| 9 | Major sixth | M6 |
| 10 | Minor seventh | m7 |
| 11 | Major seventh | M7 |
| 12 | Perfect octave | P8 |
Why “major” and “minor” and “perfect”?
The labels carry musical meaning beyond raw distance. Major intervals sound bright and open; minor intervals sound darker, more pensive. Perfect intervals (the 4th, 5th, and octave) are acoustically the most consonant — they share the strongest mathematical relationships in the overtone series, which is why they sound so stable.
The tritone (six half steps) sits exactly in the middle of the octave. It’s the most dissonant interval in Western music — so unsettling that medieval musicians called it diabolus in musica, “the devil in music,” and tried to avoid it. We embrace it now (it’s the foundation of every dominant 7th chord) but the name stuck.
Train your ear
Click two keys on the keyboard. The component names the interval between them. Then click Play interval to hear it — either as both notes at once (harmonic) or one after the other (melodic). Try the same interval starting on different notes — you’ll hear that a “perfect fifth” sounds the same no matter where it starts.
Click two keys on the keyboard.
Intervals are auditory
Reading about intervals teaches you almost nothing. Hearing them teaches you everything. A perfect fifth has a sound — open, stable, the sound of two fingers on a guitar’s lowest two strings. A minor third has a sound — the first two notes of the Star Wars imperial march, or the Greensleeves melody. Once you’ve matched a name to a sound, you’ll recognize it forever.
The next chapter explains Roman numerals — the shorthand musicians use to talk about intervals (and chords built from them) without committing to a specific key.
Recap
- An interval is simply the distance between two notes, measurable as a count of half steps.
- Intervals carry names (major third, perfect fifth, etc.) that encode not just distance but emotional quality.
- The tritone (six half steps) is the odd one out — historically called “the devil in music” for its harsh sound.
- Memorize nothing yet. Intervals attach to your ear through real music.