A clef (from the French for "key") is a musical symbol used to indicate the pitch of written notes. Placed on one of the lines at the beginning of the staff, it indicates the name and pitch of the notes on that line. This line serves as a reference point by which the names of the notes on any other line or space of the staff may be determined.

The types of clef

There are three types of clef used in modern music notation: F, C, and G. Each type of clef assigns a different reference note to the line on which it is placed.

Once one of these clefs has been placed on one of the lines of the staff, the other lines and spaces can be read in relation to it.

The use of three different clefs makes it possible to write music for all instruments and voices, even though they may have very different tessituras (that is, even though some sound much higher or lower than others). This would be difficult to do with only one clef, since the modern staff has only five lines, and the number of pitches that can be represented on the staff, even with ledger lines, is not nearly equal to the number of notes the orchestra can produce. The use of different clefs for different instruments and voices allows each part to be written comfortably on the 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 - with the important exception of transposing parts, which are written at a different pitch than they sound, often even in a different octave.

The positions of the clefs

In order to facilitate writing for different tessituras, any of the clefs may theoretically be placed on any of the lines of the staff. The further down on the staff a clef is placed, the higher the tessitura it is for; conversely, the higher up the clef, the lower the tessitura.

Since there are five lines of the staff, and three clefs, it might seem that there would be fifteen possible clefs. Six of these, however, are redundant clefs (for example, a G-clef on the third line would be exactly the same as a C-clef on the first line). That leaves nine possible distinct clefs, all of which 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 any line of the staff except the topmost, earning the name of "movable C-clef". (The C-clef on the topmost line is redundant because it is exactly equivalent to the F-clef on the third line; both ways of writing this clef have been used).

Each of these clefs has a different name based on the tessitura for which it is best suited.

In contemporary music literature, only four clefs are used regularly: the treble clef, the bass clef, the alto clef, and the tenor clef. Of these, the treble and bass clefs are by far the most common.

Individual clefs

Here follows a complete list of the clefs, along with a list of instruments and voice parts notated with them. Each clef is shown in its proper position on the staff, followed by its reference note.