How the music works

The five lines and the four gaps between them are nine neighbouring white keys. Higher on the page means further right on the piano, and a note sitting one step above another is the very next white key up. That is the whole idea — everything else is a detail on top of it.

The smallest move on a piano is to the very next key, black or white: a half step. Two of those make a whole step. A sharp raises a note by a half step and a flat lowers it, which is why the black keys have two names each — the same key, reached from either side.

Count twelve keys up from any note, black and white alike, and you land on one that sounds like it again, only higher — an octave. On the white keys that is eight of them, C up to the next C. It is the one interval every ear recognises without being taught, and it is why the keyboard is the same twelve keys repeating rather than eighty-eight different ones.

Play from C to C on the white keys and you have a major scale: whole, whole, half, whole, whole, whole, half. That pattern is what makes it sound major, not the notes themselves — start anywhere and keep the pattern and you get the same brightness in a different place.

Start on A instead and play the same white keys, and the pattern shifts: the third step is now a half step closer to the first. That one smaller gap is most of what people hear as sad. Same keys, different starting point, different feeling.

Keeping the major pattern from a note other than C means some keys have to move. Start on G and the seventh note has to be F sharp, or the pattern breaks. Rather than write that sharp on every F, the key signature says it once at the front — which is all a signature is: the accidentals this piece takes for granted.

Take a note, skip one, take the next, skip one, take the next: that is a triad, the chord almost all music is built from. On C it comes out C, E, G. Because you are skipping alternate steps, the shape looks like a snowman on the page — three noteheads stacked with no gaps.

The middle note is the one carrying the mood. Lower it by a half step and a major chord becomes minor. It is a single key's difference and it changes everything you feel about the sound, which is worth hearing rather than reading.