chapter  4
ACCIDENTALS
Pages 25

In music of the West, the octave is divided into 12 equal parts called half steps, or semitones. In non-Western music (for example, as in Middle Eastern music), the octave may be divided into 24 units (quartertones). In some more modern Western music, it may be divided into even smaller units (microtones), as in the 43-unit music by American composer Harry Partch.