What you're training
A borrowed chord — modal mixture — pulls a chord across from the parallel minor into an otherwise major-key progression. iv is the minor subdominant, same root as IV with the third dropped a half step; bVI and bVII are major triads a minor 6th and minor 7th above the tonic, both native to the minor scale and foreign to the major one. None of them push toward a target the way a secondary dominant does — they just darken the color for a bar or two before the progression resolves home. This drill trains you to catch that tint by ear.
Two levels, one skill
Level 1 asks the binary question first: in a I–x–V–I progression, was the middle chord the plain diatonic IV, or the borrowed iv? Same root, same register — only the third moves, so the whole answer rides on that one interval. Level 2 raises the bar — every round now has a borrowed chord, and you name which loan it was: iv, bVI, or bVII. Each progression resolves back through V to I, so the color always reads in context, not in isolation.
Go deeper
This drill is Trio 3 of the chromatic-harmony series — modal mixture, the parallel-minor tint borrowed chords bring to major-key harmony. The theory: modal mixture → covers where these chords come from and how they're notated. For the real-world payoff, Find borrowed chords in real music — 57 across 15 pieces, playable, labeled → lets you hear every one in context. The pushing kind of chromatic chord — applied dominants → is the other lane of this series, if you want the chord that pulls instead of the one that just tints.
Where it fits
Comfortable with chord quality and cadence resolution already? Borrowed chords are a different kind of chromaticism than secondary dominants — color, not pull. The full drill ladder has everything else.