https://www.britannica.com/art/accidentalPashkuli wrote: Fri Jan 14, 2022 12:18 pm Thus key signature symbols are accidentals... in advance. To designate a shift.
accidental, in music, sign placed immediately to the left of (or above) a note to show that the note must be changed in pitch. A sharp (♯) raises a note by a semitone; a flat (♭) lowers it by a semitone; a natural (♮) restores it to the original pitch. Double sharps (×) and double flats (♭♭) indicate that the note is raised or lowered by two semitones. Sharps or flats that are placed at the beginning of a musical staff, called a key signature, indicate the tonality, or key, of the music and are not considered accidentals.