Notation & reading
Accidental
An accidental is a sharp, flat, or natural sign placed before a note to raise, lower, or restore its pitch for the remainder of that bar.
A sharp raises a note a half step, a flat lowers it a half step, and a natural cancels either, returning to the unaltered pitch. Double sharps and double flats raise or lower by a whole step and appear where the harmony requires them. Crucially, an accidental applies to the rest of the bar at that pitch and octave, then expires at the bar line.
A courtesy or cautionary accidental, often in parentheses, restates the key signature's pitch after an accidental has expired, purely to reassure the reader. It changes nothing but prevents hesitation.
Related terms
Every term in this glossary is taught in context somewhere in Arco's curricula, on the staff, on the keyboard, and on your own fingerboard at the same time.