You’re sitting around a campfire at a party. Sooner or later the guitars come out. You grab one.
“What should we play,” you ask? Somebody names a tune. “Cool,” you say. “I don’t know that one, but what are the chord changes?” Another person tells you it’s in the key of E and starts rattling off a bunch of numbers. “Got it,” you say, nodding your head. Next thing you know, you’re making sweet, sweet music together under the moonlight.
How can people who’ve never met before play a song together, right on the spot, with zero rehearsal? Even if one of them has never even heard that song before? And what do the numbers mean?
Guitarist Melanie Faye has a great, simple explanation right here: