TIL this, thank you! I'm italian and only knew about the do re mi fa sol la si do :D

From ChatGPT:

The choice between using letter names (C, D, E, etc.) and solfege (do, re, mi, etc.) largely comes down to tradition and purpose: • Historical Convention: In Western music, the letter system has been the standard for centuries. It provides a clear, concise way to notate specific pitches on a staff, which is especially useful for instruments like the piano or guitar. • Clarity in Notation: Letters denote fixed pitches, making it easier to communicate musical ideas in written form. This helps performers quickly identify which keys or notes to play without additional context. • Educational Focus: Solfege is typically used as a tool for vocal training and ear development. It emphasizes the relationship between pitches (intervals) and is often taught using a movable system (where “do” represents the tonic of any given scale) or a fixed system (where “do” is always C). This system helps singers internalize pitch relationships and improve sight-singing. • Different Purposes: Essentially, the letter system is more suited to the precision required in written music scores, while solfege is more about developing a musician’s internal sense of pitch and harmony.

In short, both systems have their place in music, with letters serving as the backbone of Western musical notation and solfege acting as an invaluable educational tool.