Clef

A clef (from French: clef 'key') is a musical symbol used to indicate which notes are represented by the lines and spaces on a musical staff. Placing a clef on a staff assigns a particular pitch to one of the five lines or four spaces, which defines the pitches on the remaining lines and spaces.

The three clef symbols used in modern music notation are the G-clef, F-clef, and C-clef. Placing these clefs on a line fixes a reference note to that line—an F-clef fixes the F below middle C, a C-clef fixes middle C, and a G-clef fixes the G above middle C. In modern music notation, the G-clef is most frequently seen as treble clef (placing G₄ on the second line of the staff), and the F-clef as bass clef (placing F₃ on the fourth line). The C-clef is mostly encountered as alto clef (placing middle C on the third line) or tenor clef (middle C on the fourth line). A clef may be placed on a space instead of a line, but this is rare.

The use of different clefs makes it possible to write music for all instruments and voices, regardless of differences in range. Using different clefs for different instruments and voices allows each part to be written comfortably on a staff with a minimum of ledger lines. To this end, the G-clef is used for high parts, the C-clef for middle parts, and the F-clef for low parts. Transposing instruments can be an exception to this—the same clef is generally used for all instruments in a family, regardless of their sounding pitch. For example, even the low saxophones read in treble clef.

A symmetry exists surrounding middle C regarding the F-, C- and G-clefs. C-clef defines middle C whereas G-clef and F-clef define the note at the interval of a fifth above middle C and below middle C, respectively.

Common mnemonics for the notes on treble clef:

For bass clef:

Theoretically, any clef may be placed on any line. With five lines on the staff and three clefs, there are fifteen possibilities for clef placement. Six of these are redundant because they result in an identical assignment of the notes—for example, a G-clef on the third line yields the same note placement as a C-clef on the bottom line. Thus there are nine possible distinct clefs when limiting their placement to the lines. All have been used historically: the G-clef on the two bottom lines, the F-clef on the three top lines, and the C-clef on the four bottom lines. The C-clef on the topmost line has also been used, but is equivalent to the F-clef on the third line, giving a total of ten historically attested clefs placed on the lines. In addition, the C-clef has been used on the third space, i.e. not on a line at all. This is equivalent to the more common suboctave treble clef.

The ten clefs placed on lines (two are equivalent) have different names based on the tessitura for which they are best suited.