In music, an irregular resolution is resolution by a dominant seventh chord or diminished seventh chord to a chord other than the tonic. Regarding the dominant seventh, there are many irregular resolutions including to a chord with which it has tones in common or if the parts move only a whole or half step.[1] Consecutive fifths and octaves, augmented intervals, and false relations should still be avoided.[1] Voice leading may cause the seventh to ascend, to be prolonged into the next chord, or to be unresolved.[2]
The following resolutions to a chord with tones in common have been identified:
Type I is common from the 18th century; Type II may be found from the second quarter of the 19th century; Type III may be found from the mid-19th century. The composer Richard Edward Wilson is responsible for the categorization.
All three types describe a process of transforming a dominant seventh chord to a diminished seventh by raising the root by one semitone, then picking any other note in the chord and lowering it one semitone. That lowered note is now the root of a new dominant seventh chord. This works because diminished seventh chords are structurally equivalent in all of their inversions (a stack of minor thirds), so any note in a diminished seventh chord can be seen as the root note.
The most important irregular resolution is the deceptive cadence,[2] most commonly V7–vi in major or V7–VI in minor.[3] [2] Irregular resolutions also include V7 becoming an augmented sixth [specifically a [[German sixth]]] through enharmonic equivalence[3] or in other words (and the adjacent image) resolving to the I chord in the key the augmented sixth chord (FACD) would be in (A) rather than the key the dominant seventh (FACE) would be in (B).