or CLIFF, in Music, derived from the Latin word clavis, a key; because by it is expressed the fundamental sound in the diatonic scale, which requires a determined succession of tones or semitones, whether major or minor, peculiar to the note whence we set out, and resulting from its position in the scale. Hence, as it opens a way to this succession, and discovers it, the technical term key is used with great propriety. But clefs rather point out the position of different musical parts in the general system, and the relations which they bear one to another.

A clef, says Rousseau, is a character in music placed at the beginning of a stave, to determine the degree of elevation occupied by that stave in the general claviary or system, and to point out the names of all the notes which it contains in the line of that clef.

Anciently the letters by which the notes of the gamut were signified were called clefs. Thus the letter A was the clef of the note la, C the clef of ut, E the clef of mi, &c. But in proportion as the system was extended, the embarrassment and superfluity of this multitude of clefs were felt, and a better system was in time adopted.

Gui d'Arezzo, who had invented them, marked a letter or clef at the beginning of each line in the stave; for as yet he had placed no notes in the spaces. In process of time they marked no more than one of the seven clefs at the beginning of one of the lines only; and this was sufficient to fix the position of all the rest, according to their natural order. At last, of these seven lines or clefs they selected four, which were called claves signator, or discriminating clefs, because they satisfied themselves with marking one of them upon one of the lines, from which the powers of all the others might be recognized. Presently afterwards they even retrenched one of these four, namely, the gamma, of which they made use to mark the sol below, that is to say, the hypoprolambanome added to the system of the Greeks. (See Rousseau's Musical Dictionary, Malcolm on Music, and the article Music.)