Augmented 7th
aug7
0 - 4 - 8 - 10Augmented triad + minor 7th
About Augmented 7th
An augmented seventh chord is a dominant seventh with its fifth raised a semitone — in C that is C, E, G♯ and B♭, written Caug7, C7♯5 or C+7. It keeps the tritone that makes a dominant pull and adds a second point of tension above it, so it resolves harder than a plain seventh and sounds less settled on the way.
Notes and formula
The formula is 1 – 3 – ♯5 – ♭7, or 0 – 4 – 8 – 10 in semitones from the root. It is an augmented triad with a minor seventh on top, or equivalently a dominant seventh whose G has become G♯.
The chord therefore holds two unstable intervals at once: the tritone between E and B♭, which points to F, and the augmented fifth, which wants to continue upward. Both are resolved by the same destination, which is why the chord almost never appears anywhere except immediately before it.
How to play it
On piano the chord is C–E–G♯–B♭. As with any dominant, the root can be left to the bass, and E–G♯–B♭ in the right hand states everything that matters.
On guitar the workable form has the root on the sixth string: 8–x–8–9–9–x, sounding C–B♭–E–G♯. The bare augmented triad shape x32110 with a seventh added on top gives the same chord higher up the neck.
What it does
An augmented seventh is a dominant, and it behaves like one — C7♯5 goes to F much as C7 does. What changes is the strength of the pull and the colour of the bar before it: the raised fifth is a semitone below the sixth degree of the target key, so the chord contains a second leading tone alongside the usual one.
The Beatles opened Oh! Darling on this chord, and it is standard at the end of a big-band shout chorus for the same reason: when a piece needs its final dominant to sound larger than the ones before it, raising the fifth is the cheapest way to do it.
Where it sits among the altered dominants
The augmented seventh is the mildest of the altered dominants — one note changed from the plain chord. Alter the ninth as well and the chord becomes 7♯5♯9 or 7♯5♭9; alter the fifth downward instead and it becomes 7♭5.
All of them keep the third and the seventh untouched, because those two notes are what make a chord a dominant at all. Everything else in a dominant is available for colouring, and this chord is the first step along that road.
Symmetry inherited from the triad
The augmented triad inside the chord repeats every four semitones, so C, E and G♯ can each claim to be the root. Add the seventh and that ambiguity disappears — B♭ fixes C as the root — but the shape underneath still slides in four-fret steps on guitar, which is a practical way to find the chord quickly.
It also explains the chord's characteristic vagueness. For as long as the seventh is not sounding, an augmented seventh has no key at all.
Scales that contain it
The whole-tone scale contains every note of the chord and nothing that contradicts it, which makes it the standard choice. Its evenness is the reason a whole-tone run over this chord sounds weightless rather than directed.
The altered scale — the seventh mode of melodic minor — also contains the chord and adds the altered ninths. Players use it when the resolution is about to happen and the whole-tone scale when it is being delayed.
Frequently asked questions
What notes are in a C augmented 7th chord?
C, E, G♯ and B♭. It is a C7 with the fifth raised a semitone, and it is also written C7♯5.
Is aug7 the same as 7♯5?
Yes — the same four notes under two names. Charts in a jazz idiom usually print 7♯5, older sheet music prints aug7 or +7, and both mean a dominant seventh with a raised fifth.
Where does an augmented seventh chord resolve?
To the chord a fourth above, like any dominant: C7♯5 to F. The raised fifth adds a second voice pulling upward, so the resolution feels stronger than from a plain C7.