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

The letters correspond to the [white keys on a keyboard](https://www.smackmypitchup.com/smpu/content/img/MT/mtp01.gif) which are whole notes and there are 7 of them. The black keys are sharps and flats which are half steps between the whole notes.

Notice in the linked diagram, the black key between C and D is both a C sharp or a D flat and the pattern holds for the rest of the black keys.