Prolonging Tonic with V6 and Inverted V7s
Tonic prolongation refers to harmonic techniques that sustain the feeling of the tonic across several beats or measures, even when other chords appear between the opening and closing tonic harmonies. One of the simplest and most effective prolongation tools is V⁶ — the dominant triad in first inversion, with 7̂ (ti) in the bass. Because the leading tone in the bass pulls by step to 1̂ (do), V⁶ functions as a passing or neighbor chord that connects two tonic-function harmonies without asserting genuine dominant weight.
The inverted forms of V⁷ serve similar roles. V⁶₅ (V⁷ in first inversion, bass on 7̂) often moves to I or I⁶, its leading-tone bass resolving up by step while the seventh descends. V⁴₃ (second inversion, bass on 2̂, re) passes between I and I⁶ or vice versa — the bass moves by step in either direction, creating a smooth arpeggiated tonic expansion. V⁴₂ (third inversion, bass on 4̂, fa) resolves to I⁶: its bass note 4̂ descends by step to 3̂ (mi), the bass of I⁶, completing a stepwise descending line.
The key to understanding these chords as prolongations rather than cadential dominants lies in context: when they appear in the interior of a phrase and move back to a tonic-function chord, they subordinate themselves to the tonic rather than driving toward a cadence. The bass lines they generate — typically scalar or arpeggiated — are the clearest sign that prolongation, not progression, is at work. Recognizing these patterns allows analysts to identify the true structural harmonies of a phrase versus the decorative passing harmonies that fill space between them.
