Augmented sixth

This article is about the interval. For the chord, see Augmented sixth chord.

In music, an augmented sixth (Play^ⓘ), ^A6, is an interval produced by widening a major sixth by a chromatic semitone.^[1][4] For instance, the interval from C to A is a major sixth, nine semitones wide in 12 TET, and both the intervals from C^♭ to A, and from C to A^♯ are augmented sixths, spanning ten semitones (in 12 TET).

augmented sixth

Inverse	diminished third
Name
Abbreviation	A6[1], A6
Size
Semitones	10
Interval class	2
Just interval	125:72,[2] 225:128,[3] 7:4[citation needed], 59049:32768[citation needed]
Cents
12-Tone equal temperament	1000
Just intonation	955, 977, 969, 1020

Augmented sixth Play^ⓘ.

Being augmented, it is nominally considered a dissonant interval, even though it renders a perceptibly consonant harmonic seventh in some tuning systems:^[5] In septimal meantone temperament, an augmented sixth is specifically assigned to the harmonic seventh (a consonant just interval of 7:4) and very nearly so in quarter comma meantone and 31 TET. In 12 TET, the augmented sixth is equal to ten semitones, and is both nominally and audibly dissonant.

An augmented sixth (^A6) is enharmonicly equivalent to a minor seventh (m7). An inverted ^A6 is a diminished third.

Description

The augmented sixth is relatively rare. Its most common occurrence is built on the lowered submediant of the prevailing key, in which position the interval assumes a natural tendency to resolve by expanding to an octave built on the dominant tonal degree. In its most common and expected resolution, the lower note of the interval moves downwards by a minor second to the dominant while the upper note, being chromatically inflected, is heard as the leading note of the dominant key, rising naturally by a minor second. It is the strong tendency to resolve in this way that properly identifies this interval as being an augmented sixth rather than its more common enharmonic equivalent: The minor seventh, which has a tendency to resolve inwardly.

As the augmented sixth is correctly named only in certain specific contexts, and the notational distinction between ^A6 and the minor seventh (m7) is often ignored. Regardless of the true diatonic context, many composers and annotators instead favor the more familiar minor seventh – especially in chord notation which biases towards notation as major and minor thirds, in which chords containing a nominal ^A6 are always notated as seventh chords.

The augmented sixth interval in combination with certain other intervals forms the group of chords known collectively as augmented sixth chords.

The just augmented sixth arises in the extended C major scale between A♭ and F♯.^[6] Play^ⓘ

See also

• Augmented sixth chord
• List of meantone intervals