Complete Encyclopaedia of Music/A/Accidentals

Accidentals. Sharps, flats, and naturals are called accidentals because they are used tc change the sound of letters, as the chord, of which these letters are a part, may require ; and because they affect the sound of the letters upon which they are set no farther than the compass of the bar in which they are enclosed. If there be occasion for them in a succeeding bar, they must be again renewed ; but if one measure ends and the next begins with the same note, the accidental character which alters the first note is understood to affect the second. Those flats, and sharps, and naturals which are seen al the commencement of a movement are not accidentals, but are called the Signature, and denote the key in which the piece is to be performed. A sharp, flat, or natural, frequently implies some change of key, or different modulation from that in which the piece commenced, and some consider these signs as equally affecting the key, whether found at the commencement or in the progress of the tune. But we generally designate the flats, sharps, &c., at the beginning, as the signature, and such as come afterwards in the music as accidentals.

In turns, sometimes the first of the four notes composing it, and at other times the third, are required to be semitones; in which case they must be expressed by an accidental either above or below the sign of the turn, thus:, ,. The German theorists place the accidental above when the first note is required to be a semitone, and when the third note is a semitone they place the accidental below, as in the above example.