The idea
You take chords from the parallel mode (same tonic) and use them in the main key. In C major the most used reservoir is C minor (C D Eb F G Ab Bb).
Borrowed chords in C major
- From C minor Aeolian: Fm (iv), Ab (bVI), Bb (bVII), Eb (bIII), Dm7b5 (iiø), Gm (v), Fm6, Abmaj7.
- From C Phrygian: Db (bII), Dbmaj7.
- From C Lydian: D (II), D/C.
- From C Mixolydian: Bb (bVII), Gm7 (v7).
- From C Dorian: F7 (IV7), Dm7 stays, Ebmaj7.
Berklee courses group Fm, Dm7b5, Abmaj7, Bb7 as the minor subdominant: they all contain Ab, which falls to G.
Typical formulas
- C – F – Fm – C: the minor plagal, immediate emotion.
- C – Ab – Bb – C: bVI–bVII–I, an “epic” cadence (from video games and rock).
- C – Bb – F – C: Mixolydian rock.
- Am – F – Fm – C: chromatic descent A–Ab–G in the inner voices.
Melody
The melody must adapt: over Fm you don't sing A but Ab or C. The change from A to Ab in the topline is precisely the moment that strikes.
Real example
“Creep” by Radiohead (1992, in G): G – B – C – Cm. The Cm is the iv borrowed from G minor. In C it would be C – E – F – Fm. The coda of “Hey Jude” (Beatles, in F) alternates instead F – Eb – Bb – F, with Eb as the Mixolydian bVII.