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{{About|the interval|the chord|Augmented sixth chord}}
{{use dmy dates|date=June 2025}}
{{Infobox Interval
| main_interval_name = augmented sixth
| inverse = [[diminished third]]
| complement = [[diminished third]]
| other_names =
| abbreviation = A6,<ref name="B&S"/> {{sup|{{sc|A}}}}6
| semitones = 10
| interval_class = 2
| just_interval = 125:72,<ref name=Haluska>{{cite book |last=Haluska |first=Jan |year=2003 |title=The Mathematical Theory of Tone Systems |page={{mvar|xxvi}} |ISBN=0-8247-4714-3 }} — "Classic" augmented sixth.</ref> 225:128,<ref>{{harvp|Haluska|2003|at="Augmented sixth"}}</ref> 7:4{{citation needed|date=August 2024}}, 59049:32768{{citation needed|date=August 2024}}
| cents_equal_temperament = 1000
| cents_24T_equal_temperament = 
| cents_just_intonation = 955, 977, 969, 1020
}}

[[File:Augmented sixth on C.png|thumb|right|Augmented sixth {{audio|Minor seventh on C.mid|Play}}.]]

In [[music]], an '''augmented sixth''' ({{Audio|Minor seventh on C.mid|Play}}), '''{{sup|{{sc|A}}}}6''', is an [[Interval (music)|interval]] produced by [[Augmentation (music)|widening]] a [[major sixth]] by a [[chromatic semitone]].<ref name="B&S">{{cite book |last1=Benward |first1= |last2=Saker |first2= |year=2003 |title=Music: In theory and practice |volume=I |page=54 |ISBN=978-0-07-294262-0 }} — {{sup|{{sc|A}}}}6 not specificly given, but general example of augmenting major intervals described.</ref><ref>{{cite book |last=Hoffmann |first=F.A. |year=1881 |title=Music: Its theory & practice |pages=89–90 |publisher=Thurgate & Sons }} — Digitized 16&nbsp;Aug 2007. Uses archaic terms '''superfluous sixth''' or '''extreme sharp sixth'''.</ref> For instance, the interval from C to A is a [[major sixth]], nine semitones wide in {{nobr|[[12 equal temperament|12 {{sc|tet}}]],}} and both the intervals from C{{sup|{{Music|b}}}} to A, and from C to A{{sup|{{music|sharp}}}} are augmented sixths, spanning ten semitones (in [[12 equal temperament|12 {{sc|tet}}]]).

Being [[Augmentation (music)|''augmented'']], it is nominally considered a [[consonance and dissonance|dissonant]] interval, even though it renders a perceptibly consonant [[harmonic seventh]] in some tuning systems:{{sfnp|Benward|Saker|2003|p=92}}
In [[septimal meantone temperament]], an augmented sixth is specifically assigned to the [[harmonic seventh]] (a [[consonance and dissonance|consonant]] [[just intonation|just interval]] of [[harmonic seventh|7:4]]) and very nearly so in [[quarter comma meantone]] and {{nobr|[[31 equal temperament|31 {{sc|tet}}]]}}. In {{nobr|[[12 equal temperament|12 {{sc|tet}}]],}} the augmented sixth is equal to ten semitones, and is both nominally and audibly [[consonance and dissonance|dissonant]].

An augmented sixth ({{sup|{{sc|A}}}}6) is [[enharmonic]]ly equivalent to a [[minor seventh|minor seventh (m7)]].
An [[inverted chord|inverted]] {{sup|{{sc|A}}}}6 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 (music)|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, naturally tending to rise by a minor second.
It is the strong tendency to resolve in this way that properly identifies an interval as functioning harmonically as an augmented sixth rather than a minor seventh, its more common enharmonic equivalent: The minor seventh has a contrary tendency to resolve to a lower pitch.

As the augmented sixth is correctly named only in certain specific contexts, and the notational distinction between {{sup|{{sc|A}}}}6 and the [[minor seventh|minor seventh (m7)]] is often ignored. Regardless of the true [[diatonic]] context, and despite the augmented sixth being harmonically consonant in several tuning systems, many [[composer]]s and [[musical notation|annotators]] to the contrary favor the more familiar but dissonant minor seventh – especially in chord notation, which is biased towards rendering chords as chains of major and / or minor thirds, in which chords containing a nominal {{sup|{{sc|A}}}}6 are conventionally [[musical notation|written]] as the near-equivalent flattened [[seventh chord]]s.

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

The just augmented sixth arises in the extended C&nbsp;major scale between A{{sup|{{music|b}}}} and F{{sup|{{music|#}}}}.<ref>{{cite book |last=Paul |first=Oscar |year=1885 |section="Pythagorean major third" (musical interval) |title=A Manual of Harmony |quote=for use in music-schools and seminaries, and for self-instruction |page=165 |publisher=Theodore Baker |translator-first=G. |translator-last=Schirmer |translator-link=G. Schirmer |section-url=https://books.google.com/books?id=4WEJAQAAMAAJ&q=musical+interval+%22pythagorean+major+third%22 |via=Google }}</ref> {{audio|Just augmented sixth in scale.mid|Play}}

==See also==
* [[Augmented sixth chord]]
* [[List of meantone intervals]]

==References==
{{reflist|25em}}

==Further reading==
* {{cite book |last=Hewitt |first=Michael |year=2000 |title=The Tonal Phoenix: A study of tonal progression through the prime numbers three, five, and seven |publisher=Orpheus-Verlag |ISBN=978-392262696-1 }}

{{Intervals}}

[[Category:Augmented intervals]]
[[Category:Sixths (music)]]