The letter names used here, C through B, belong to a fixed-pitch naming system distinct from the movable-doh solfège syllables, Do, Re, Mi and so on, that most people associate with singing a scale. Solfège descends from the monk and music theorist Guido of Arezzo, working in the early eleventh century, who drew the syllables Ut, Re, Mi, Fa, Sol and La from the first syllables of successive lines of a Latin hymn to John the Baptist, Ut queant laxis, as a mnemonic for teaching singers to find pitches relative to one another rather than as fixed, absolute notes. Ut was later replaced by Do in most traditions, and Ti was eventually added to complete the seven syllable set.
The letter-name system C, D, E, F, G, A, B is older still in its basic logic, descending from the Latin alphabet letters used by Boethius and other late antique and early medieval theorists to mark absolute pitches, and it survives today as the standard naming convention in English, German and several other European musical traditions, run alongside the solfège syllables rather than replacing them; a singer trained in movable-doh solfège reads the same pitch C as Do only when the piece is in the key of C major, since solfège names a scale degree rather than a fixed pitch.