Definition
A triad is in first inversion when its third is in the bass. The intervals above the bass are a third and a sixth, hence it is called a six chord (figured 6, or 6/3). In C major: I6 = C/E, IV6 = F/A, V6 = G/B, ii6 = Dm/F. The first inversion is less stable than root position but more stable than the second: it is the ideal chord for making the bass singable and for prolonging a function.
Doublings
| Chord | Recommended doubling | To avoid |
|---|---|---|
| I6, IV6 | root or fifth; the third (in the bass) is possible | — |
| V6 | root or fifth | the third (it is the leading tone, in the bass) |
| ii6 | often the bass (the third, fourth degree): reinforces the predominant function | — |
| vii°6 | the third (second degree, in the bass) | the root (leading tone) |
General rule: do not double notes with an obligatory tendency (leading tone, altered notes); in all other cases the first inversion offers more freedom than root position.
Typical functions
- I6: prolongs the tonic and lets the bass move (I–I6–IV, I–V–I6).
- V6: “soft” dominant, with the leading tone in the bass rising to the tonic (V6–I). Frequent at the beginning of phrases.
- ii6: the most-used predominant before the cadence (ii6–V–I), with the bass F rising to G.
- IV6: with the A in the bass it leads by step to the V; it is the typical chord of the descending bass C–B–A–G harmonized I–V6–IV6–V.
- vii°6: weak dominant, a passing link between I and I6 (C–D–E in the bass).
Chains of sixths
A series of parallel six chords moving by step (called fauxbourdon in the Middle Ages and Renaissance) produces a fluid line without parallel fifths, because between the bass and the upper voices there are only thirds and sixths. In four voices, however, you must alternate the doublings, otherwise parallel octaves or fifths arise in the inner voices. The safest way is to write in three real voices and add the fourth voice with different doublings at each chord.
Practical rules
- Use the first inversion when the bass has to move by step between two root-position chords.
- A V6 must not resolve to a chord with the bass falling: the leading tone in the bass must rise.
- At the end of a concluding phrase prefer root position: a cadence on I6 sounds open.
Common mistakes
- Doubling the leading tone in the V6.
- Using too many consecutive six chords in four voices with the same doubling: hidden parallels.
- Ending a piece on a six chord thinking it is “the same” as the tonic.
Examples
- The Beatles, “Let It Be”: C–G/B–Am: the V6 (G/B) creates the stepwise descent in the bass C–B–A.
- Procol Harum, “A Whiter Shade of Pale”: a stepwise descending bass supported by chords alternating between root position and inversions, inspired by Baroque basses.
- Pachelbel's Canon in versions with a stepwise bass: D–A/C#–Bm.
- Bach chorales: the ii6 before the cadence is almost a stylistic signature.
- In Corelli's trio sonatas, chains of sixths animate the descending sequences.
How to use it in composition
- To write a bass line that “sings,” alternate root position and first inversion: you get stepwise motion instead of leaps.
- In pop, the first inversion is written as a slash chord (C/E, G/B): it is the simplest way to make progressions sound professional.
- A chain of descending sixths in strings or woodwinds creates an elegant cascade, ideal for transitions.
Exercise
- Write in D major I – V6 – IV6 – V – I (bass D–C#–B–A–D) in four voices and check the doublings.
- Write a chain of six descending six chords in three voices, then add the fourth voice, varying the doublings.
- Reharmonize a root-position pop loop with at least two first-inversion slash chords.
Connections
Chord inversions and six and six-four chords; Triads and inversions; Inversion figures; The six-four chord; Slash chords and inversions in pop; Rule of the octave.