☞ The clefs are three in number, called the C, F, and G clefs, and are probably corruptions or modifications of these letters. They indicate that the letters of absolute pitch belonging to the lines upon which they are placed, are respectively C, F, and G. The F or bass clef, and the G or treble clef, are fixed in their positions upon the staff. The C clef may have three positions. It may be placed upon the first or lower line of the staff, in which case it is called soprano clef, upon the third line, in which case it called alto clef, or upon the fourth line, in which case tenor clef. It rarely or never is placed upon the second line, except in ancient music. See other forms of C clef under C, 2.