3.1 The natural sign

A third accidental is the natural, ♮, which cancels out a preceding sharp or flat. Example 5 contains four notes. The second of these is an F with a sharp next to it, designating a raised F; namely, the black key to the right of F on the keyboard. The fourth note is an F with a natural sign next to it, designating F natural, the white note.

Example 5 A natural sign cancelling a sharp. This example is presented on a solitary treble staff rather than on a grand staff, since all of the music is in the treble clef

In staff notation, the modification introduced by an accidental is generally valid for the length of a bar, a segment of music delineated by the vertical lines that cross the staff, as shown in Example 6. There are three bars in the example. In the first bar, the second note has a flat next to it, so it is a B flat. This flat sign remains active until the next bar line unless a natural sign is introduced, so the fourth note is also a B flat, even though there is no flat sign next to it. The sixth note in the bar, also a kind of B, has a natural sign next to it. This cancels the preceding flat and makes the sixth note a B natural.

The second and third bars of the example also contain Bs. In the second bar, the first B has no accidental next to it, so it is a B natural. The fifth note, however, has a flat next to it, so it is a B flat. That B flat gets cancelled by the bar line that soon follows, so the first note in bar three needs a flat next to it to make it a B flat, too.

Example 6 A passage of notated music featuring bar lines and accidentals