Let's begin by reviewing the most frequent seventh chord constructed above scale degree 7, the V65. The chord progressions below should be very familiar:
Exchanging scale degree 6 for 5 yields new harmonic possibilities.
The principle of mixture makes possible the following non-diatonic variants:
Note that the root position leading-tone seventh chord is fully diminished and contains TWO dissonant elements above the bass: a diminished 7th and a diminished fifth. Resolving both dissonant elements results in a root position tonic chord. This characterisitic voice leading will help us determine how leading-tone 7th chords function in inversion.
The resultant half-diminished and fully diminished seventh chords produced by operations 1 and 2 are called leading-tone seventh chords. Although these chords all sound different, their voice leading characteristics are quite similar. As the next example shows how leading-tone 7th chords function very much like linear dominant chords.
In fact, the first three positions (root position, first, and second inversions) differ
by only one note to their corresponding inversions of V7
viio7 (V65) as lower neighbor to I
viio65 (V43) passing between I and I6
Only the viio42(see below) does not correspond to any inversion of V7. Knowing, however, that this chord almost always resolves to V64 , can you explain its harmonic function?