Continuing the discussion from Minor Keys, Roman numerals:
@HertzDevil, thank you for pointing this out, and I feel like this is an important enough subject to deserve its own thread.
The question arises, what is the most useful way for us to store chord information for Hooktheory Trends?
As you have noted, Hooktheory currently stores data in the relative major mode. We chose this because we felt that the majority of progressions in popular music are either in the major mode, or ambiguous enough that analyzing them in the major mode is satisfactory. For songs that are properly in a different mode, the relationships between chords would be preserved (e.g., vi → IV of the ionian mode and i → ♭VI of the aeolian mode are counted as the same trend).
However, there are also disadvantages to this approach. Organizing borrowed chords is not ideal. We’ve done our best to group borrowed chords together enharmonically, but are still missing many cases. Furthermore, some people are interested in “major key” or “minor key” perspectives: for example, comparing the mixolydian progression I → ♭VII to the ionian progression I → ♭VII rather than the ionian progression V → IV.
This method also has the effect of improperly categorizing songs that are written in parallel modes by borrowing chords (although perhaps this is just a symptom of a different issue).
As a specific example, to find the relative frequency of the ♭VII, I assumed that an adequate representation would be a combination of: borrowed chords that are enharmonic to ♭VII, applied IV/IV chords, and IV chords coming from theoryTabs in the mixolydian mode. I didn’t count V chords in the aeolian mode (or any “minor i” modes) since @trevordeclercq was referring to a “major key” usage of ♭VII. However, I also didn’t include Lydian mode progressions that would be technically equivalent, because I simply forgot to consider this possibility. Ultimately this was a little cumbersome.
Off the top of my head, I see a few ways of proceeding:
Keep chord data the same: Here the goal would be to fix theoryTabs that are improperly analyzed in parallel modes (by perhaps enabling a transpose to parallel mode feature), and do a better job of grouping enharmonic chords together. This is in effect an ionian mode-centric approach.
Separate trends by modes: Here we could simply not compare chord progressions across modes. This would give better data on how chords are used in a specific mode, but the downside is that there would be far less data (over 90% of TheoryTabs are in the ionian mode).
Organize chord data by parallel major mode: Here, progressions like I → ♭VII would be counted the same in both the ionian and mixolydian modes. This would also in effect separate modes in to two groups: major-I modes and minor-i modes. One clear advantage of this is having no difference between chords borrowed from a mode and the chords that are in that mode. I suppose this was in effect what I had to do to find statistics on ♭VII. Here, rather than storing the borrowed mode, we would instead store the label in the “popular” style notation, which is consistent across modes.