The second inversion of a chord is the voicing of a triad, seventh chord, or ninth chord in which the fifth of the chord is the bass note. In this inversion, the bass note and the root of the chord are a fourth apart which traditionally qualifies as a dissonance. There is therefore a tendency for movement and resolution. In notation form, it is referred to with a c following the chord position (For e.g., Ic. Vc or IVc) or as a 6
4 chord (as in I6
In the second inversion of a C-major triad, the bass is G -- the fifth of the triad -- with the root and third stacked above it, forming the intervals of a fourth and a sixth above the inverted bass of G, respectively.
In the second inversion of a G dominant seventh chord, the bass note is D, the fifth of the seventh chord.
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Cadential second-inversion chords are typically used in the authentic cadence I6
4-V-I, or one of its variation, like I6
4-V 7-I. In this form, the chord is sometimes referred to as a cadential 6
4 chord. The chord preceding I6
4 is most often a chord that would introduce V as a weak to strong progression, for example, making -II-V into II-I6
4-V or making IV-V into IV-I6
The cadential 6
4 can be analyzed in two ways: the first labels it as a second-inversion chord, while the second treats it instead as part of a horizontal progression involving voice leading above a stationary bass.
In a progression with a passing second-inversion chord, the bass passes between two tones a third apart (usually of the same harmonic function). When moving from I to I 6, the passing chord V6
4 is placed between them - though some prefer VII 6 to V6
4 - creating stepwise motion in the bass (scale degrees - - ). It can also be used in the reverse direction: I 6-V6
4-I. The important point is that the V6
4 chord functions as a passing chord between the two more stable chords. It occurs on the weaker beat between these two chords. The upper voices usually move in step (or remain stationary) in this progression.
In a progression with an auxiliary second-inversion chord, the IV6
4 chord functions as the harmonization of a neighbor note in the progression, I-IV6
4-I. In this progression, the third and fifth rise a step each and then fall back, creating a harmonization for the scale degrees - - in the top voice.
In this progression, the bass arpeggiates the root, third, and fifth of the chord. This is just a florid movement but since the fifth is present in the bass, it is referred to as a bass arpeggiation flavour of the second inversion.
The chord does not act as an inversion of I 5LCC MT50 A444 1989.
3; it serves neither to extend it nor to substitute for it.