What you're training
A secondary dominant — also called an applied chord — is the dominant of a chord other than the tonic, borrowed in to pull harder toward that chord. V7/V is the dominant of the dominant; V7/IV tonicizes the subdominant; V7/vi tonicizes the relative minor. This drill trains you to catch the moment one shows up — a chord that doesn't belong to the key, reaching for somewhere new before the progression resolves home.
Two levels, one skill
Level 1 asks the binary question first: was that progression entirely diatonic, or did one chord get borrowed? Level 2 raises the bar — every round now has an applied dominant, and you name which chord it was pulling toward. Every progression resolves the applied chord into its target before the cadence continues home, so the pull is always audible, not just theoretical.
Go deeper
This drill is one lane of three on secondary dominants. The theory: tonicization → covers why these chords work and how they're notated. For the real-world payoff, Find them in real pieces → surveys 635 applied chords across 57 real pieces — V7/V is the most common at 88 appearances, then V7/IV at 69, V7/vi at 56, and V7/iv at 51 — and lets you play through them. Train the ear here, learn the theory there, then go find it in the music.
Where it fits
Comfortable with chord quality and cadence resolution already? Secondary dominants are the next layer — the same dominant-to-tonic pull you already hear, just aimed at a chord other than home. The secondary dominants reference has the five-minute theory recap, and the full drill ladder has everything else.