In music terms, what does "Do is always C" imply?

The statement "Do is always C" refers specifically to the fixed Do system, where the solfège syllable "Do" consistently corresponds to the note C, regardless of the key in which a piece of music is being played. This system provides a stable reference point for singers and musicians, allowing them to identify pitch relationships in a consistent manner. In this framework, "Do" is not affected by the key signature or the scale being used; it retains its identity as the note C.

This fixed approach contrasts with the movable Do system, where "Do" might represent different notes depending on the key of the piece. In movable Do, "Do" would represent the tonic (or first note) of any given scale, which could vary from piece to piece. However, in the fixed Do context, the note C always holds the position of "Do," providing a reliable structure for learning and performance.