tritone

The tritone is an interval spanning six semitones, or three whole tones. It is also known as the augmented fourth or the diminished fifth, depending on the context and spelling. In equal temperament it measures exactly 600 cents and is one of the most distinctive dissonances in Western harmony. The interval is enharmonically equivalent, meaning it can be written as either an augmented fourth or a diminished fifth.

In tuning systems other than equal temperament, the exact ratios of the two notes forming a tritone can differ, but the acoustic distinction between the two spellings remains a matter of notation and harmonic function rather than pitch class alone. The tritone is symmetric within an octave: if you invert it, you again obtain a tritone.

Historically, the tritone was viewed as highly dissonant and was often avoided in early counterpoint. It gained reputation as “the diabolus in músico” in medieval and Renaissance music. As harmony developed, composers used the tritone for expressive tension, especially in cadences and chromatic progressions.

In tonal harmony, the most common appearance of the tritone is inside the dominant seventh chord, between its third and seventh degrees (for example, B and F in a G7 chord). This tritone resolves by half steps to the tonic, driving cadential motion. In modern music, the tritone remains a powerful color interval and underlies techniques such as tritone substitution, where a dominant chord is replaced by another a tritone away to create rich, flexible harmonic progressions.