Common practice accidental duration rule
In common practice, an accidental affects all notes of the same pitch in the same octave within the same bar, unless it is cancelled by another accidental. If it is not cancelled, it is automatically cancelled in the following bar.
To ensure that the cancellation is unambiguous, it is customary to add a cautionary accidental to the first note of the same pitch in the following bar.
In common practice, the accidental of a note in one bar is automatically cancelled in the following bar. For example, in the key of G major, if an F♮ is in one bar, an F in the following bar shows a sharp sign, even though the sharp is already implied by the key signature.
When using the common practice accidental duration rule by default, Dorico Pro also displays cautionary accidentals, which are restatements of an earlier accidental. They are considered optional; that is, they are neither explicit confirmations nor cancellations, but help to eliminate ambiguities. Cautionary accidentals are also known as courtesy accidentals.
Cautionary accidentals are shown in the following circumstances:
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Subsequent notes within the same bar have the same note name in different octaves.
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Subsequent notes in the following bar have the same note name in the same octave.
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The first occurring note in the following bar has the same note name in any octave.
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Augmented/Diminished or double-diminished/augmented intervals are identified within the same bar.
For each of these situations, you can choose whether cautionary accidentals are shown in parentheses, shown without parentheses, or not shown at all.