Augmented fourth

An augmented fourth is an interval of six semitones.

The interval between C and F#, for example, is an augmented fourth as it contains six semitones.

An interval of six semitones is also known as "tritone" (three tones).

In a lot of common scales, such as the standard major scale and the natural minor scale, the interval between the root on the scale and the fourth note on the scale is equal to five semitones. This more common interval is called a perfect fourth. The augmented fourth is "augmented" as it is one semitone larger than this more common interval. The augmented fourth is a "fourth" if it occurs between the first and the fourth note on a scale (or more generally between two notes with two notes in between).

In principle, an augmented fourth is the same as a diminished fifth. Both intervals contain six semitones. An augmented fourth through would refer to the interval between the root on a scale and the fourth note on the scale (or more generally between two notes with two notes in between) whereas a diminished fifth would refer to the interval between the root on a scale and the fifth note on the scale (or more generally between two notes with three notes in between).

The augmented fourth occurs naturally, for example, in the Lydian scale. The Lydian in F is F, G, A, B, C, D, E and the interval between F and B is equal to six semitones.

See also:
Intervals on the chromatic scale, Intervals on the chromatic scale (index)

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