Mutation

What it means

In medieval solmisation the notes are arranged in six-note series, the hexachords, named with the syllables ut, re, mi, fa, sol, la. Melodies, however, often extend beyond six notes. The singer then changes to another hexachord and renames a common note: a note called "la" in the first hexachord becomes "re" in the second, and the melody can continue. This change is called mutation.

Musical use

The hexachords began on G, C or F and overlapped, so that there were many common notes. Mutation therefore works like a pivot. It was taught until the Renaissance and is associated with Guido of Arezzo and his school, who developed solmisation further. With the rise of the major–minor system it lost importance.

Mutation should be distinguished from the change of voice at puberty, which bears the same name in some languages, and from modulation, the change of key: mutation concerns only the naming of syllables.

Performance practice

When you practise medieval melodies with solmisation, first find the common notes of the hexachords and deliberately sing the new syllable at those points. In this way you hear the transition and understand how singers organized intervals in their heads.