with the tied note. Under this system, the notes in the example above are: 1: G, G, G (the sharp carries over) m. 2: G (with courtesy accidental), G, G (the flat carries over) m. 3: G (which is tied from the previous note), G, G (the natural sign cancels the sharp sign) Though this convention is still in use particularly in tonal music, it may be cumbersome in music that features frequent accidentals, as is often the case in atonal music. As a result, an alternative system of note-for-note accidentals has been adopted, with the aim of reducing the number of accidentals required to notate a bar. According to Kurt Stone, the system is as follows: Accidentals affect only those notes which they immediately precede. Accidentals are not repeated on tied notes unless the tie goes from line to line or page to page. Accidentals are not repeated for repeated notes unless one or more different pitches (or rests) intervene. If a sharp or flat pitch is followed directly by its natural form, a natural is used. Courtesy accidentals or naturals (in parentheses) may be used to clarify ambiguities but are kept to a minimum Because seven of the twelve notes of the chromatic equal-tempered scale are naturals (the "white notes", A; B; C; D; E; F; and G on a piano keyboard) this system can significantly reduce the number of naturals required in a notated passage. Occasionally, an accidental may change the note by more than a semitone: for example, if a G is followed in the same measure by a G, the flat sign on the latter note means it is two semitones lower than if no accidental were present. Thus, the effect of the accidental must be understood in relation to the "natural" meaning of the note's staff position. In some atonal scores (particularly by composers of the Second Viennese School), an accidental is notated on every note, including natural notes and repeated pitches. This system was adopted for "the specific intellectual reason that a note with an accidental was not simply an inflected version of a natural note but a pitch of equal status." Double accidentals Double accidentals raise or lower the pitch of a note by two semitones, an innovation developed as early as 1615. This applies to the written note, ignoring key signature. An F with a double sharp applied raises it a