Modal Cadence Options

Question

I understand that when playing in a mode, the cadences are quite different from tonal cadences. For example, in the Phrygian mode a cadence would be IV - iii (or II - i if we're renumbering the chords).

Q: What are all of the cadence options for all of the major modes?

Answer 1

Our three major modes are Ionian, Lydian, and Mixolydian. The Roman numerals for these are:

Ionian
I  ii  iii  IV  V  vi  vii°

Lydian
I  II  iii ♯iv° V  vi  vii

Mixolydian
I  ii  iii° IV  v  vi ♭VII

You'll notice that both Ionian and Lydian have a major V chord, meaning that the standard cadence of V–I is possible in these two major modes. (Whether it's the most common, I can't answer.) Perhaps due to Mixolydian's minor v chord, the ♭VII is often substituted as a dominant, resulting in a ♭VII–I cadence.

If we generalize it to all modes, it seems that the hierarchy of cadential harmony goes something like:

1. V where possible (Ionian, Lydian)
2. ♭II where possible (Phrygian) (maybe there's something to be said about tritone substitutions here?)
3. ♭VII where possible (Dorian, Mixolydian, Aeolian, sometimes Phrygian)

The only mode missing here is Locrian, which many (myself included) don't even consider an adequate mode based on the diminished tonic triad.