A Dictionary of Music and Musicians/Mutation

by William Smyth Rockstro

MUTATION. (Lat. Mutatio, from muto to change.) I. When, in the Solmisation of a Plain Chaunt Melody, it becomes necessary to pass from one Hexachord to another, the process by which the transfer is effected is called a Mutation. [See Hexachord.] In ascending from the Hexachordon durum to the Hexachordon naturale, the change may be conveniently made by substituting the re of the latter for the sol of the former, at the note D—whence this particular Mutation is known as that of Sol Re. [See example, vol. i. p. 734b.]

In descending from the Hexachordon naturale to the Hexachordon durum, the sol of the latter must be taken, instead of the re of the former, at the same note; and the Mutation is then called Re Sol. The same process will also serve for the mutual interchange between the Hexachordon naturale and the Hexachordon molle, at the note G.

But, in ascending from the Hexachordon naturale to the Hexachordon durum, the re of the latter must be substituted for the la of the former, at the note A, by means of the Mutation La Re: and, in descending from the Hexachordon durum to the Hexachordon naturale, the la of the second will be sung instead of the re of the first—Re La.

Direct communication between the Hexachordon durum, and the Hexachordon molle, is rarely used, on account of the False Relation described under the head of Mi Contra Fa.

Many different systems of Mutation have been recommended by early writers; but all agree in the necessity of so arranging that the Semitone shall always fall between the Syllables mi and fa. Lucas Lossius (Erotemata musicæ, 1563) directs the change to be always made by means of re in ascending, and la in descending; and enforces his rule in the following distich—

Vocibus utaris solum mutando duabus:
Per re quidem sursum mutatur, per la deorsum.

II. The term is also applied to the change which takes place in a Boy's Voice, when it passes from Treble, or Alto, into Tenor, or Bass. The period of this transformation is uncertain; but it generally declares itself between the ages of fourteen and sixteen, and is very rarely deferred later than the completion of the seventeenth year. During the time that it is in progress, the vocal organs undergo so much disturbance, that great care is necessary in order to prevent them from being seriously injured by incautious exercise.

III. More rarely, the word is used to denote that change in the position of the hand upon the Violin, which, by English Violinists, is called the Shift.

[ W. S. R. ]