Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The tritone is a musical interval that spans three whole tones. The tritone, sometimes known as the Diabolus in Musica, is the same as an augmented fourth, which in 12-tone equal temperament is enharmonic to a diminished fifth. It is often used as the main interval of dissonance in Western harmony, and is important in the study of musical harmony. "Any tendency for a tonality to emerge may be avoided by introducing a note three whole tones distant from the key note of that tonality."