Nadege Roche-Labarbe on Nostr: i've been reading your post for five minutes and I'm confused. I'm French, and I have ...

i've been reading your post for five minutes and I'm confused. I'm French, and I have never heard about those letters in my piano lessons or solfège lessons. To me, do re mi fa sol la si do are the names of the notes. And do is always a do. Why would you call them with letters instead? I mean what's the difference, can you explain? I've seen those letters written on sheets for jazz and rock music and anything coming from the US and modern instruments like the guitar, I assumed that they were strictly equivalent to do re mi... no??