This has come up a couple of times in recent threads, and there's been a bit of confusion about how it works, so I thought I'd run it again, and invite comments. I KNOW there've been several other threads over the years dealing with it,(I probably started some of them) but current folks seem to appreciate current opinions so here goes.I first saw this system used when I was performing in Nashville in the late seventies. The studio guys (and I do mean 'Guys') would scribble the 'numbers' down on the inside of matchbooks (so much cooler than a hunk of sheet music on a stand in front of them), lick the matchbook (ugh) and stick it on the mike stand (or their knee), and then play the new song as if they'd known it for years. Note: It doesn't indicate 'melody', merely the chord structure for them to improvise over.
Make the number '1' the key you're in. eg: Key of C = #1.
1,2,3,4,5,6,7 = C,D,E,F,G,A,B.
A minor chord is indicated by a 'minus' sign. A diminished chord is indicated by a small 'circle'. Sharps and flats use the music notation symbols. Augmenteds have a small '+' sign. Regular numbers of bars have no symbol, but 'repeat signs' are used when needed. A 'split' bar has a '/' between chords.
Sevenths, sixth's etc. are not designated because it's assumed the musician knows where they'd be appropriate.
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Please note (cause this often comes up) I don't think that this is a "Foolproof" system, and there are many musical situations it DOESN'T cover. What it DOES do, is allow you to write an almost instant chart for pretty simple or complex songs, allowing others (who've learned the numbers) to play with you. I learned it in about 10 minutes.....but it took several months before I was comfortable with it in keys other than C,D,G,A, and E.
It's damn good theory training though, cause you have to learn your sharps and flats (and their numbers) to play in the 'harder' keys. Here's a simple example of the number system in action. I'll use Paxton's "Can't help but Wonder Where I'm Bound", 'cause most folks know it. Let's do it in the key of "D" (Therefore D is number 1)
1 4/2- 5 1/5 1 4/2- 5 1
2-/5 1/6- 2-/5 1
The chord equivalent is:
D////G//Em//A7////D//A7//D////G//Em//A7////D////
Em//A7//D//Bm//Em//A7//D////
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Hope it's of some use. Cheers
Rick