Same four chords, pop or rock depending on where you start

On the Guitarshelf catalog, Rock in A minor (variant) — chord change and Pop in C (with barre) — chord change look like they share nothing: different styles, different keys, opposite moods. And yet they use the exact same four chords, in the exact same cyclical order.

The same loop, just shifted by one step

The pop sheet runs C-G-Am-F. The rock sheet runs Am-F-C-G. Line the two sequences up side by side: it's the same four-chord loop turning continuously, just read starting from a different point — the rock sheet starts exactly where bar three of the pop sheet already is.

This isn't an isolated coincidence

C-G-Am-F (or any rotation of it) is arguably the most recycled progression in modern pop: popularized as the "Axis progression" by the Australian comedy group Axis of Awesome's mashup medley, it runs through dozens of otherwise unrelated hits, from "Don't Stop Believin'" to "With or Without You" to "Take On Me." It's not a secret formula: it's a precise balance between staying inside a single key (easy to play, easy to sing over) and having enough harmonic motion to feel like it's going somewhere.

Why the starting point changes everything

A four-chord loop doesn't inherently say which chord is "home" — the tonic. Started and ended on C, the loop sounds firmly major and upbeat: that's the pop sheet. Started and ended on Am, the exact same chords sound minor and more wistful: that's the rock sheet. Nothing changed in the notes; only the point where the ear settles as "home" changed — and that point alone decides whether a grid sounds pop or rock.

Practice it

The best way to hear it is to play both sheets back to back: Pop in C (with barre) first, making sure to land on the C chord at the end of each loop, then Rock in A minor (variant), this time landing on Am. Same fingers, same chords, same changes — and yet two pieces that don't sound alike at all.