Understanding tones, semitones and intervals

How far apart are two notes? On a piano, the answer is easy to see: count the keys you step through to go from one to the other. Count every key, black and white, without skipping any, and don’t count the key you start from.

From C to E, that gives four: C♯, D, D♯, E. From E to G, only three: F, F♯, G. Both look like “two white keys apart”, yet one is longer than the other. That is why musicians count all the keys and not just the white ones.

Direction does not change anything: from E down to C, you also pass four keys (E♭, D, D♭, C). The most common slip is to count the starting key as well, which adds one too many.

Each of those steps has a name: a semitone, the distance from one key to the very next one. It is the smallest distance on the piano. Most of the time a semitone goes from a white key to a black key, or the other way round; but E–F and B–C are semitones between two white keys, because no black key sits between them.

Two semitones make a tone: you skip one key. C to D is a tone (C♯ sits between them), and so is E to F♯. In American books you will also read “half step” and “whole step”: they mean the same thing. In this guide we stick to semitone and tone.

Scales are built from these two steps. The C major scale, on the white keys from C to C, goes tone, tone, semitone, tone, tone, tone, semitone: its two semitones are E–F and B–C. That pattern is what the guide on first scales builds on.

The distance between two notes is called an interval. Intervals are named by counting note names, including both ends. From C to E you go through C, D, E: three names, so it is a third. From C to G, five names: a fifth. From C to the next C, eight: an octave, the same note name, higher.

The count of semitones then gives the exact size. C to E is 4 semitones, a major third. E to G, from the first section, is also a third, but only 3 semitones: a minor third. A chord is minor when the third above its root, the note that names it, is this smaller one: C to E♭ rather than C to E. C to G is 7 semitones, a perfect fifth; C to C, 12.

The other intervals are named the same way: C to D is a second, C to F a fourth, C to A a sixth, C to B a seventh. You will meet them soon enough; the third, the fifth and the octave come first because chords are built from them.

An interval can be heard two ways. Played one after the other, it is a small piece of melody: your ear follows the jump. Played together, it becomes a small piece of harmony: the two sounds blend, more or less smoothly. A semitone played together rubs; an octave almost melts into one note. Many listeners describe the fifth as open or hollow; trust your own ears and find your own words.

Press two keys below to measure them, then listen both ways. Black keys are named with flats here (D♭ rather than C♯); both names are right. When you are ready, switch to the challenges: you get a starting key and a number of semitones, and look for the arrival.

Thirds and fifths are the building blocks of chords: a major chord is a root, a major third and a perfect fifth. That is the next step, in how to build a chord.