Spell the scale

This is the most useful rule in the whole course: EVERY MAJOR AND MINOR SCALE USES EACH OF THE SEVEN LETTERS EXACTLY ONCE, IN ALPHABETICAL ORDER.

So you never have to memorise a scale. Write the seven letters starting from the root — G, A, B, C, D, E, F — and then adjust each accidental until the W W H W W W H pattern fits. The letters were never in doubt.

It also explains something the keyboard hides. G♭ major contains a C♭, which is the same key as B. Why not just call it B? Because the letter C has to appear exactly once, and B is already taken.

The same rule quietly rules some keys out. D♯ major would need an F double-sharp, so nobody writes in D♯ major — they write E♭ major instead. Those keys are simply not in this course.

Seven letters, each used once — then fix the accidentals

G♭ major: G A B C D E F, every letter once — so the 4th is C♭, not B.

Practise this in the trainer — it opens with this lesson the first time the concept comes up.