(1) In the narrow sense, the medieval Western European practice of singing melodies on the syllables ut, re, mi, fa, sol, and la, which were introduced by Guido d’Arezzo to designate the degrees of a hexachord; in the broad sense, any method of singing melodies by articulating the syllabic names of the degrees of some scale (relative do) or the names of the tones corresponding to the tones’ absolute pitch (fixed do); a method of teaching singing from notation.

In his system of solmization, Guido used the initial syllables in the lines of a hymn for the feast of St. John the Baptist as the names of the degrees, at the same time preserving the lettered designations of the absolute pitch of the tones A, B, C, D, E, and F. Each solmization syllable designated a certain degree of a hexachord independent of the degree’s absolute pitch, whether in a natural hexachord (from the tone C), a soft hexachord (from the tone F), or a hard hexachord (from the tone G). The transition of a melody from one hexachord to another required changes, or mutations, in the syllabic names of the tones. The introduction in the late 16th century of the syllable si to designate the seventh degree of a scale made mutations within the same key unnecessary.

In the late 17th century, the syllable ut was replaced by do, which was easier to sing. In countries where Romance languages were spoken, in Russia, and later in the USSR, solmization syllables were subsequently used to designate the absolute pitch of tones (fixed do). In countries where Germanic languages were spoken and in Hungary, these same syllables with slight alterations are used as movable syllables (movable do), and the tone letters are used to designate the absolute pitch of tones. In the Estonian SSR and Latvian SSR, the movable syllables used are jo, le, mi, na, so, ra, di (in Estonia) and ti (in Latvia).

(2) In Russian, the cognate sol’mizatsiia is sometimes used to designate the rhythmic reading of notes without intonation, as distinguished from solfeggio.