Linear six-four chords are second inversion triads with the 5^th of the chord in the bass. The bass is always doubled. The brackets indicate that these chords have a dependent, embellishing function as neighbor tones, passing tones, or arpeggiated prolongations.

Voice leading

A. Neighboring Six-Four Chords: [IV ] and [I  ]

1. [IV ] has do in the bass, which is doubled, and functions as a neighbor chord to I. The chord is created through the occurrence of two simultaneous neighbor tones (s – l – s and m – f – m) with the doubled 5^ths remaining stationary. If the chord occurs at a cadence, it functions as a plagal cadence (see the chapter on Cadences).

2. The cadential [I  ] has so in the bass, which is doubled. It functions as a neighbor chord between V – V or V – V⁷ Inc.

B. Passing Six-Four Chords: [V ] and [I ]

1. [V ] has re in the bass, which is doubled. It functions as a passing chord between I and I⁶, producing a voice exchange (d – r – m or m – r – d) between the bass and one of the upper voices: I – [V ] – I⁶ or I⁶ – [V ] – I.

2. [I ] has so in the bass, which is doubled. It functions as a passing chord between IV and IV⁶, producing a voice exchange (f – s – l or l – s – f) between the bass and one of the upper voices: IV – [I  ] – IV⁶ or IV⁶ – [I ] – IV.

All the above keyboard voicing examples can be converted into open spacing.

C. The Arpeggiated Six-Four Chord 

Each of the primary triads can be prolonged by an arpeggiated bass figuration that alternates root position, first inversion, and second inversion triads.