About accidentals

Courtesy accidentals

Although a barline is nowadays understood to cancel the effect of an accidental (except for a tied note), often publishers will use a courtesy accidental (also referred to as a cautionary accidental or a reminder accidental) as a reminder of the correct pitch if the same note occurs in the following measure. This usage varies, although a few situations are construed to require a courtesy accidental, such as

* when the first note in a measure is one which had had an accidental applied in the previous measure
* after a tie carries an accidental across a barline, when the same note appears again in the subsequent measure.

Other uses are inconsistently applied.

Courtesy accidentals are sometimes enclosed in parentheses to emphasize their nature as reminders.