In music theory, a natural (♮) is an accidental which cancels previous accidentals and represents the unaltered pitch of a note.
It can be used as key signature or accidental. An example of an A note with an accidental in place is shown below.
A note is natural when it is neither lowered nor raised by flat (♭) or sharp (♯) (or double-flat or double-sharp ). Natural notes are the notes A, B, C, D, E, F, and G represented by the white keys on the keyboard of a piano or organ. On a modern concert harp, the middle position of the seven pedals that alter the tuning of the strings gives the natural pitch for each string.
The scale of C major is sometimes regarded as the central, natural or basic major scale because all of its notes are natural notes, whereas every other major scale in the circle of fifths has at least one sharp or flat in it.
The notes F♭, C♭, E♯, B♯, and most notes inflected by double-flats and double-sharps correspond in pitch with natural notes; however, they are not regarded as natural notes but rather as enharmonic equivalents of them and are just as much chromatically inflected notes as most sharped and flatted notes that are represented by black notes on a keyboard.
The natural sign is derived from a square b used to denote B♮ in medieval music (in contrast with the round b denoting B♭, which became the flat symbol). The Unicode character MUSIC NATURAL SIGN '♮' (U+266E) should display as a natural sign. Its HTML entity is ♮.
In musical notation, a natural sign (♮) is a sign used to cancel a flat or sharp from either a preceding note or the key signature. But, naturals are assumed (by default) in key signatures and mentioned only in key signature changes.
When used as an accidental, it is written to the left of the note head.
When used as an accidental, it is applied to the note after the natural sign in the same octave in the same bar.
A double natural is a symbol that has two naturals (♮♮).
In a case where one needs to cancel both flats or sharps of a double flat or double sharp, it is acceptable to write a single natural (♮). In older practice, two naturals (♮♮) could be written. (It's a 'double natural' sign.)
Similarly, to cancel one flat or sharp from a double flat or double sharp, the traditional convention is to use (♮♭ or ♭♮) or (♮♯ or ♯♮) respectively, but the naturals are generally omitted in modern notational practice.
Theoretically, the same principle could be considered when canceling the symbol of a triple sign or beyond.
A ♮♭ can be also written when changing a sharp to a flat. Similarly, a ♮♯ can be also written when changing a flat to a sharp.