Chords & Harmony

Six-Four Chord

Definition

A six-four chord is a triad in second inversion, with its fifth in the bass, such as C/G. Its fourth above the bass makes it unstable, so classical harmony uses it in a few set patterns: cadential, passing and pedal.

A six-four chord is a triad in second inversion: its fifth is in the bass. C/G (G–C–E) is a six-four chord, named after its figured bass figures, 6/4, because E is a sixth and C a fourth above the bass G. In Roman numerals it is written with ⁶₄, as in I6/4.

Why it is special

In common-practice harmony the fourth above the bass is treated as a dissonance. That makes a six-four chord sound unsettled, as if it is leaning toward something else, so composers rarely use it as a free-standing chord. Instead it appears in a few standard patterns, each with its own job. In all of them, the bass note is usually the doubled note.

Three grand-staff panels. Cadential, in 4/4, three bars: whole-note F4 A4 C5; half notes E4 G4 C5, then D4 G4 B4; whole-note E4 G4 C5; bass F2, G2, G2, C3; labeled IV, I6/4, V, I. Passing, in 3/2, half notes in four voices: soprano E5 D5 C5, alto G4 G4 G4, tenor C4 B3 C4, bass C3 D3 E3; labeled I, V6/4, I6. Pedal, in 3/2, half notes: soprano E5 F5 E5, alto G4 A4 G4, tenor C4 C4 C4, bass C3 C3 C3; labeled I, IV6/4, I. — Cadential: IV – I6/4 – V – I; over the G in the bass, C and E fall to B and D. Passing: I – V6/4 – I6, the bass walking C–D–E while the soprano walks E–D–C. Pedal: I – IV6/4 – I over a held C, with E–F–E and G–A–G above it.

The cadential six-four

The most important one. Just before a cadence the bass arrives on the dominant note (G), but the upper voices still hold C and E. Then they slip down to B and D, turning the chord into V: the sixth above the bass falls to a fifth and the fourth falls to a third. The six-four sits on a stronger beat than the V that follows, and it makes the arrival on the dominant feel weightier. Because it really decorates V, many theorists label it V6/4–5/3 rather than I6/4.

The passing six-four

Here the bass passes by step between two positions of another chord: I – V6/4 – I6, with the bass walking C–D–E. The six-four falls on a weak beat, and the upper voices often move against the bass, as in the voice exchange in the example (C–D–E in the bass, E–D–C in the soprano).

The pedal six-four

Over a held bass note, two upper voices step up and back: C – F/C – C, with E–F–E and G–A–G above a C bass. The middle chord, IV6/4, is a neighbor chord over a pedal. It is common at the end of hymns, as a gentle plagal color.

Other six-fours

In accompaniment patterns such as a waltz bass, the left hand may touch the fifth of a chord on its way through (sometimes called an arpeggiated six-four). It is part of a broken chord rather than a separate harmony.

Practice with The 6/4 chord: three jobs and Name the 6/4 chords.

Common questions

Why is a six-four chord considered unstable?

Because of the fourth above the bass. Traditional harmony treats that fourth as a dissonance that should resolve, so a second-inversion triad sounds as if it is leaning toward another chord.

What is a cadential six-four?

A second-inversion tonic chord (I6/4) over the dominant bass note just before a cadence. Its upper notes fall by step to form V, so it works as a decoration of the dominant chord.