ELI5, why are the musical notes represented by letters in some places (C-D-E-F-G-A-B), but in others by their sound (do-re-mi-fa-sol-la-si-do) ?

Question

I’m from Mexico and the way I learned the musical notes was by their sound, however some friends from other places learned the notes with letters.

In: Other

Answer 1

I believe these two things are not the same actually. While C-D-E etc. are absolute note values (a certain pitch), the do-re-mi scale is relative to a base tone. So if you start a major scale from G, then do will be G, re will be A, mi will be B etc.

So one denotes fixed pitches, while the other denotes relative pitches to a base tone.