Why does ii˚ and ii˚6 lead to V in minor when all they really want to do is resolve to III?

Question

In tonal harmony, in the minor mode the subdominant chords built on ^2 and ^4 are diminished chords. The root position ii˚ is usually not used in minor unless it falls on a weak beat but even when it is both the ii˚ and the ii˚6 chord have the same tritone interval which obviously wants to resolve to III and not to V. Yet in tonal harmony the staple progression is a ii˚6 chord moving to a V chord. Why does this happen and is there not another way in minor mode to have subdominant harmony without a tritone that doesnt resolve?

Answer 1

There are two important elements:

1. Root movement by descending fifth: this is the quintessential harmonic motion in Tonality, V -> I being the prime example, but ii -> V being no less important. One learns to hear and anticipate this harmonic progression such that even in minor iio -> V feels natural — arguably even more natural that iio -> III, in spite of the logic that suggests otherwise.
2. iio and V7 have two common tones: ^2 and ^4. ^b6 naturally wants to move to ^5. So, between the two common-tones and the natural resolution, one has a near-complete V7 chord. ^2 can be doubled so that one of them moves to the leading tone; and if not, the fact that ^2 has been heard will still help fill out the V chord.

Answer 2

ii˚6 chords most commonly have their 3rds doubled, so they are 1 note away from being iv chords with doubled roots. As a result, both ii˚6 and iv chords can be resolved to V chords in similar ways (these examples are in C minor, notes are stacked in SATB order from top to bottom):

iv-V:

A♭ -> G

F -> D

C -> B

F -> G

ii˚6-V:

A♭ -> G

F -> D

D -> B

F -> G

Quite a lot of chords that are 1 note away from the iv chord end up similarly being resolved directly to V chords. One of the most striking examples is the ♭II a.k.a. Neapolitan chord:

♭II6-V:

A♭ -> G

F -> D

D♭ -> B

F -> G

Yes, the Wikipedia article on the Neapolitan chord says that this D♭ -> B movement is somehow permitted in traditional voice leading.

To answer "is there not another way in minor mode to have subdominant harmony without a tritone that doesnt resolve", the iv chord, which has no tritones, keeps its subdominant function in minor keys, including the ability to resolve to the tonic chord without incident.