A Dominant 7th Chord: Notes, Voicings, and How to Play It

The first four bars of a slow change blues in A sit on this chord and nothing moves. Every textbook says a dominant seventh is unstable and has to go somewhere, and here is a whole tradition parking on one for a third of the form. A7 holds both jobs at once: it is home in a blues and it is the chord that drags a piece of music into D, and only what follows it decides which.

Try It: A7 in the Chord Finder

Set the root to A, sound the major triad, then add G on top and hear the chord lean forward.

The Notes of A7

Written out: A, C♯, E, G. One accidental, and it lands on a black key where you would expect it.

The G is the trap. A major as a key carries three sharps, F♯, C♯ and G♯, so a player reading in it has been raising every G for pages. A7 asks for a G natural, which means the chord does not belong to the key of A major at all. It belongs to D. Beginners who reach for A7 as a fancier tonic in an A major song are hearing that clash without being able to name it.

How A7 Is Built

Take A major, A, C♯ and E, and add the note a minor 7th above the root. The chord stays major, but the new note manufactures an interval that was not there before: C♯ up to G is six semitones, a diminished 5th, and that tritone is the engine. Lower the C♯ to C and you have Am7, with no such tension. Raise the G to G♯ and you get Amaj7, a different animal.

The tritone is also the instruction. C♯ is a semitone below D and pulls up, G a semitone above F♯ and pulls down. Move both and you land on D and F♯, two thirds of a D major triad, with the A free to stay where it is.

A7 on the Piano

Only one of the four notes is black, and the hand crosses it early: thumb on A, index back on C♯, then out to E and G, both white, the little finger ending on the white key directly below the octave. Right hand 1, 2, 3, 5 fits without argument. The span from A to G is a minor 7th, comfortably inside a small hand, which is one reason this is usually the first seventh chord a pianist owns.

The resolution is worth practising as a two-finger exercise before it is a chord. Hold A2 alone in the left hand and take only C♯ and G in the right, index and little finger. Move each a semitone in opposite directions: C♯ steps up onto D, the white key immediately to its right, and G steps down onto F♯, the black key just above and to its left. The geography is mirrored between the two voices, black to white going up and white to black coming down, and once the fingers have felt it they stop needing to think about it.

A7 on the Guitar

Open A major is the shape guitarists complain about, three fingertips crowded into one fret across three neighbouring strings. A7 solves it by subtraction. Lift the middle of those three fingers off the third string and x 0 2 0 2 0 is the whole chord: two fretted notes with a vacated string between them, so neither finger can lean on its neighbour. What that finger was holding was a duplicate of the bass, and what replaces it is the open third string sounding G.

Low to high the shape gives A2, E3, G3, C♯4, E4. Three of the five sounding strings are open, which is why it rings so much longer than a barred seventh does. The tritone sits in the middle of the voicing on adjacent strings, the open G against the C♯ at the second fret. With the G underneath, the interval reads as an augmented 4th and wants to open outward, so the G falls to F♯ and the C♯ climbs to D as the chord gives way.

Two variants earn their keep. x 0 2 0 2 3 adds a second G on the first string, a harder sound that suits a blues. x 0 2 2 2 3 keeps the full A major fingering and adds the little finger instead, restoring the doubled root for a rounder folk cadence.

Away from the nut it is the E7 shape barred at the fifth fret, 5 7 5 6 5 5. For comping, drop everything except the notes that carry the meaning: 5 x 5 6 x x is root, seventh and third on the sixth, fourth and third strings, no fifth at all, and it is light enough to be struck and released.

The key rewards guitarists more than most. A twelve bar blues in A needs A7, D7 and E7, which take two, three and two fingers, all in the first position. Move the same blues to E and the V chord becomes B7, four fingers and a stretch. Differences that small decide a great many keys on this instrument.

Inversions

The third inversion is the useful one, because its bass note already sits a semitone above where the music is going. Play 3 0 2 0 2 0 on a guitar, the open shape with the sixth string at the third fret, and the bass falls straight onto D/F♯ at 2 0 0 2 3 2, a line descending A, G, F♯ while the top of the chord barely moves.

The first inversion is where the guitar runs out of hands: the fifth string is this chord’s natural bass, and putting C♯ there at the fourth fret uses up the finger that should be holding the root above. On a keyboard it costs nothing.

Voicings

Which Keys Contain A7

• V of D major
• V of D harmonic minor
• V of D melodic minor
• I of A mixolydian
• VII of B natural minor
• IV of E dorian

The first three are one fact stated three times: whichever kind of D a piece is in, this is the chord that announces it. B natural minor is the opposite case. It holds the same seven notes as D major, so A7 lives there too, but on the seventh degree with nothing to resolve to, and folk rock uses it exactly that way, as a colour rather than a signpost.

Where A7 Shows Up

The third row is where this chord does its most interesting work. G major contains no C♯ at all, so an A7 dropped into a song in G is exactly one note out of the key. The other three are native, and the one it carries at the top is G itself, the tonic of the key it has supposedly just left. The diatonic chord on the second degree of G is Am, a mild thing that goes almost anywhere. Sharpen its third to C♯ and it acquires a leading tone aimed at D, and for the length of one chord the ear takes D as home. Then D reverts to being the V of G and hands you back. That borrowed C♯ is the whole mechanism, a leading tone manufactured for a key you are only visiting. Lead sheets often print II7 rather than V/V, the same idea with the analysis left out.

The ragtime turnaround chains the trick. B7, E7, A7 and D7 are four dominant sevenths walking round the circle of fifths into G, each the dominant of the next, and A7 is the link at which the chain comes back within sight of the key.

The blues row explains why singers end up here whether the key suits their range or not. All three chords have first position shapes with open bass strings, so the accompaniment rings underneath the singing instead of being fretted flat. That the tonic is a dominant seventh offends the textbook and nobody minds, because the flattened seventh belongs to the melody here as much as to the harmony.

Related Chords

• A Major Chord the triad this is built on
• A Major 6th Chord x 0 2 2 2 2 against x 0 2 2 2 3, one fret apart and a world away in function
• Secondary Dominants and Borrowed Chords for the V/V job in detail
• Seventh Chords: The Complete Guide
• The ii, V, I Progression in Practice

Learn More

• Diatonic Chords: A Beginner’s Guide
• Extended Chords and Jazz Harmony
• Chord Inversions and Voice Leading
• The Circle of Fifths Explained