I–V–vi–IV (the ‘Axis’) by Ear

4 moves — and 2 other loops your ear will offer first.

The progression drill loads here.

The I–V–vi–IV (the ‘Axis’) loop moves 4 times: I → V → vi → IV. Heard once, in a key nobody announced, what you are actually tracking is where the weight falls — which chord feels like an arrival and which one feels like it is still leaning.

Mistaken forvi–IV–I–V (the same loop, started one chord further round); I–vi–IV–V (50s Doo-Wop) (the same chords, arriving in a different order).

That is the whole difficulty of loop recognition: the set of chords is common property, and the only thing separating one famous loop from another is the order they arrive in and the one you come to rest on.