Prolongation using the Leading-Tone Chord
The leading-tone triad (viiº in major, viiº in minor) and its seventh-chord forms (viiº⁷ and viiø⁷) share three of their four pitches with V⁷, making them functionally equivalent to the dominant. When they appear between two tonic harmonies — typically moving from I to I or from I to I⁶ — they act as neighbor or passing chords that prolong the tonic zone rather than initiating an authentic cadential motion.
The most common prolongation pattern involves viiº⁶ (leading-tone triad in first inversion, bass on 2̂, re). Its bass note 2̂ often appears between two statements of 1̂ (do) as an upper-neighbor bass, while the soprano and inner voices remain on or near the tonic pitches. This creates a momentary harmonic stir that enriches the texture without destabilizing the tonic. The first-inversion placement is critical: root-position viiº or viiº⁷ is strong enough to assert dominant function and approach a cadence, but first inversion subordinates the chord to the surrounding tonic.
In minor keys, the diminished-seventh chord (viiº⁷) built on the raised 7̂ (ti) is especially colorful because it divides the octave into four equal minor thirds — a fully symmetrical stack. This chord appears both as a prolongation and, in its inverted forms, as a leading-tone approach to any chord a minor second above one of its pitches. Understanding which version of the leading-tone chord is present — and whether it is in first inversion or root position — is the key to determining whether prolongation or cadential function is at work.
