From the Borrowed Chords theory, I should be able to use the flat-third major (bIII) in my composition and it should sound good. However, after many trial and errors, I am unable to discover any suitable chord progression that utilizes the flat-third major pleasingly. Does anybody know how to apply the flat-third major chord into a song?
It's fairly 'in yer face', and works best in blues and soul. Think 'Knock on Wood', often used between I and IV.Good as a turnaround , I-bIII- II- bII -I, first four in the last bar of sequence.
You say 'I can use'. You can use anything you like in your songs - they don't have to obey any rules or theory. They may well do, but they don't have to. If it sounds good...
In a minor key, you can use: i - bIII - bVII - IV. Since this is minor key, the flats are redundant, but I like to include them anyway, for clarity. Several songs use this progression, but one that comes to my mind is "Radioactive" by Imagine Dragons (Bm-D-A-E). I'm not at a keyboard, but I'd imagine the same progression would work reasonably well if you replaced i with I.
From a functional harmony perspective, bIII seems to have a tonic function.
Use the BVII chord as well. That nice fourth interval between BIII and BVII helps to move there nicely, or at least to set zit it up tonaly, thirds can be a nasty jump. Jarring if nothing else so nice sundomiant to tonic, IV-I or related BVII/ ii - I, can really smooth that out. Also minor iv. The licc helps
The basic classical theory is that borrowed chords have the same function as the diatonic chords for which they substitute. So, borrowed minor
iv still functions as a subdominant.
But you might consider a different theory if you are dealing with rock music. Some rock music used chord roots based on a minor scale, but chromatically makes the chord qualities on those roots major. In other words, roots
bIII come from the minor orientation of a lot of rock music, but chords are harmonized with major thirds. It's a bit similar to how blues adds minor sevenths to
I IV V even though those tones aren't in the "key."
This post discusses the style with one textbook source calling in "chromatic minor."
From this perspective
bIII isn't borrowed. It's part of a different, unique tonality.