eli5: in music, since there are 12 notes per octave, why are only 7 letters used instead of 12?

Question

eli5: in music, since there are 12 notes per octave, why are only 7 letters used instead of 12?

In: 15

Answer 1

Scales in “western music” typically have 8 notes. Each scale has different intervals between the notes that split the 12 notes (semi-tones) into the 8 required for that scale – so the intervals (in semi-tones) for a major scale go 2,2,1,2,2,2,1. For a minor scale it goes 2,1,2,2,2,2,1.

Every scale is made up of every letter – A to G once and once only. If the interval lands on either a sharp or a flat, then you choose which to call it based on what letters you need for that scale.

For example, the D major scale goes D, E, F#, G, A, B, C#, D.

Here, the F# is also a Gb, and the C# is also a Db. However D, E, Gb, G, A, B Db, D has 2 Gs and 2 Ds, so isn’t considered “correct”.

So there are only 7 letters because that’s what you need to correctly notate each scale.