Intervals: the Building Blocks
Every chord, every melody, every harmony you’ve ever heard is really just a set of distances between notes. Musicians have a name for that distance: an interval. Learn to measure intervals in semitones and you have the one skill that unlocks chords, scales, and melodies all at once.
What is an interval?
An interval is simply the number of semitones between two notes, counted from the lower note up to the higher one. It doesn’t matter which two notes you pick — C to E, or F♯ to A♯ — if the distance is 4 semitones, it’s the same interval with the same name and, importantly, the same sound character. That’s the powerful part: once you recognize an interval by its distance, you recognize it everywhere, on any root.
The interval names you need
Each semitone distance has a standard name. Here are the ones that come up constantly:
| Semitones | Name | Example from C |
|---|---|---|
| 1 | minor second (m2) | C → C♯ |
| 2 | major second (M2) | C → D |
| 3 | minor third (m3) | C → D♯ |
| 4 | major third (M3) | C → E |
| 5 | perfect fourth (P4) | C → F |
| 7 | perfect fifth (P5) | C → G |
| 8 | minor sixth (m6) | C → G♯ |
| 9 | major sixth (M6) | C → A |
| 10 | minor seventh (m7) | C → A♯ |
| 11 | major seventh (M7) | C → B |
| 12 | perfect octave (P8) | C → C |
Notice the pattern in the names: “major” intervals and “minor” intervals usually come in pairs exactly one semitone apart, with the minor version being the smaller of the two.
The pair that matters most: thirds
Of everything in that table, the major third (4 semitones) and minor third (3 semitones) deserve special attention, because that single semitone difference is what separates a major chord from a minor chord. Every triad you’ll build in this course starts with a root, then stacks either a major or minor third on top — get that one interval right by ear and by count, and you’re most of the way to reading any chord.
The perfect fifth (7 semitones) matters too, but for a different reason: it stays the same whether the chord is major or minor, so it acts as a stable frame rather than a mood-setter.
Counting quickly on the keyboard
The fastest way to check an interval is to count keys, including black ones, between the two notes — never skip a key, and never count the starting note as “1.” A shortcut: a major third is “up 4,” which on white-key-heavy stretches often lands you on the next white key past one black key; a minor third is “up 3,” one semitone shorter. When in doubt, count semitone by semitone rather than trusting the shape by eye.
Common mistakes to avoid
- Counting letter names instead of semitones. C to E is “three letters away” (C, D, E) but it’s 4 semitones — letter-counting and semitone-counting give different numbers for the same interval.
- Mixing up which interval is bigger. A minor third (3) is smaller than a major third (4) — “minor” means fewer semitones here, not a different starting point.
- Losing count across black keys. Every key you pass, black or white, is one semitone. Slow down and count them individually until it becomes automatic.
Now play
This round mixes major and minor chords, which means every root can go either way — the third could be 3 semitones up or 4. Your job is to hear and count the difference in real time: build the third first, check whether it’s 3 or 4 semitones from the root, and let that tell you whether you’re building major or minor. That single distinction is the whole game this round.