The major scale

Every major scale follows the same steps, W-W-H-W-W-W-H, so a scale that starts on G is forced to use one black key, F♯.

A ladder of whole and half steps

Sing do, re, mi, fa, sol, la, ti, do and you have sung a major scale. A scale is a set of notes in order, and the major scale is the one that most Western songs are built from, from nursery tunes to symphonies. What makes it major is the spacing between its notes, not the note it starts on. Going up, the steps are whole, whole, half, whole, whole, whole, half, usually written W-W-H-W-W-W-H. That gives eight notes and seven steps, and the first and last notes share a letter name one octave apart.

A scale takes its name from that first note, accidental included. A scale that starts and ends on B♭ is B♭ major, and B major is a different set of notes. Play C to C on the white keys and the pattern falls into place by itself: the two half steps land on E to F and B to C, the only white-key pairs with no black key between them. That is why C major is the one major scale with no sharps or flats.

Building G major step by step

Start the same pattern on G and something has to change. G to A is a whole step, A to B a whole step, B to C a half step, C to D a whole step, D to E a whole step. The sixth step must be another whole step, but E to F is only a half step on the keyboard. To keep the pattern, F is raised to F♯. The last step, F♯ to G, then comes out as a half step, exactly what the pattern asks for. So G major is G, A, B, C, D, E, F♯, G, with one sharp.

Why call that note F♯ and not G♭? On the piano they are the same key, but a scale uses each letter name once, in order. G major already has a G, so its seventh note must use the letter F. The rule can look fussy until you read music: with one letter per step, every note of the scale sits on its own line or space, and the scale climbs the staff evenly.

Going the other way: F major

Start on F and the problem shows up earlier. F to G and G to A are whole steps, but the third step must be a half step, and A to B is a whole step. Lowering B to B♭ fixes it: A to B♭ is a half step, and B♭ to C is a whole step. F major is F, G, A, B♭, C, D, E, F, with one flat. Some starting notes need sharps, some need flats, and some need several. Each major scale has its own fixed set, and a later unit puts all of them on one circle.

A practical way to check a scale you wrote: count the half steps between neighbouring notes on the keyboard and compare them with 2-2-1-2-2-2-1. Those numbers add up to 12, one octave. If a step comes out as 3 or 0, a letter is wrong or an accidental is missing. Try it on the keyboard below by following G major from G to G, and listen for the half step from F♯ up to G at the top.