In the video How To Analyze Songs from the channel 12 tone, the guy wisely separates the task of labeling from analyzing. There's a comment where he lists some possible analysis options of the label bIII:
Chromatic mediant of the root
- Passing chord between ii and iii
- New root in a direct modulation
- Chromatic mediant of the V chord
- Tritone substitution resolving to ii
- Secondary-axis substitute for V chord
- Secondary dominant of tritone substitution of V chord
- It's all just atonal
- Someone also says: part of an extended plagal cadence bIII bVII IV I
I'd like to know, how a bIII (the Eb chord in the key of C) functions different when analyzed as a modal interchange chord and a chromatic mediant chord? And also how would you differentiate the chromatic mediant of V and of I. I thought chromatic mediant was just a label of a chord distant a minor/major third apart from a degree (not being diatonic), but aparently there's also a semantic issue involved because a chord would "function" as a chromatic mediant and not as a modal borrowing. What should I look for to determine this classification? Thanks.
I believe the "Chromatic mediant" wikipedia article shed some light on my question.
"Some chromatic mediants are equivalent to altered chords, for example ♭VI is also a borrowed chord from the parallel minor (...), with context and analysis revealing the distinction."
And that was exactly my question: What to look for in the context to distinguish both? The article quotes:
"Chromatic mediants (...) provide color and interest while prolonging the tonic harmony, proceed from and to the tonic or less often the dominant"
So, is "being surrounded by the same chords" a necessary condition for a chord to receive the chromatic mediant terminology?