C clef

Its centre marks the staff line that is middle C.

A clef is the sign at the left of each staff that tells you which line stands for which note. Treble and bass clefs almost always stay in one place; the C clef is the one that still moves. Its two bowls meet at a point, and whichever line that point sits on is middle C, the C near the middle of a piano keyboard. Counting lines from the bottom, on the third line the result is called the alto clef; on the fourth line, the tenor clef. That is the question most people bring here, and the glyph alone cannot answer it: 𝄡 in a message is a C clef with no line underneath.

The sign is a stylised letter C. As staff notation took shape around the 11th century, scribes wrote a letter at the start of the line to fix one pitch, usually F or C, and read the rest from it. Centuries of copying by hand reshaped the C into the bracket-like form you see now. In Spanish, Italian and Portuguese, where the note C is called do, the same sign is the do clef.

Who actually reads music in the C clef?

Viola players every day; cellists, bassoonists and trombonists when the music climbs.

The viola is the one common orchestral instrument whose usual clef is the C clef, in its alto position, which is why "viola clef" is another name for the alto clef. Cello, bassoon and trombone normally read bass clef and switch to the tenor clef (C on the fourth line) for high passages, which saves the little ledger lines that pile up above the staff. That is the main reason the clef moves: keep a part's notes on the five lines instead of above or below them.

Vocal music once used it even more. Soprano, mezzo-soprano and baritone parts had their own C clefs on the first, second and fifth lines, and old choral scores and some scholarly editions still show them. Those positions faded over the 18th and 19th centuries as choirs moved to treble and bass clefs, leaving alto and tenor as the two you will meet.