Why does the music disc have “So” and “Ti” instead of “Sol” and “Si”?

In Romance languages (Spanish, Portuguese, Italian, etc.) notes are named with solfège syllables—DO, RE, MI, FA, SOL, LA, SI, DO.

The solfège system used in many countries—including the United States—was revised in the 1800’s so that all notes begin with a different letter. The 7th note Si was replaced with Ti. And all became 2 letter notes: Sol became So.

In American-, and British-English, the solfège syllables are DO, RE, MI, FA, SO, LA, TI, DO.