12 bar blues

[apple pie]

are the 3 chords used for the 12bar blues A9 E9 and C9?

[Brewer14]

Depends on what key you're playing in.

http://guitar.about.com/library/weekly/aa112100c.htm

[mono12]

The chords are

I (16x) IV (8x) I (8x) V (4x) IV (4x) I (4x) IV (4x)

I means the first note of the scale your in, so in E thats E. That means IV is A and V is B.

so the chords in E are

E (x16) A (x8) E (x8) B (x4) A (x4) E (x4) (B x4)

You can play straight major chords or 7ths or 9ths or minor or whatever.

[jake plays guitar]

twelve bar blues are great for jamming on.

[xhaereticusx]

The chords are

I (16x) IV (8x) I (8x) V (4x) IV (4x) I (4x) IV (4x)

I means the first note of the scale your in, so in E thats E. That means IV is A and V is B.

so the chords in E are

E (x16) A (x8) E (x8) B (x4) A (x4) E (x4) (B x4)

You can play straight major chords or 7ths or 9ths or minor or whatever.
There are much more basic progressions than that.

|I|I|I|I|
|IV|IV|I|I|
|V|IV|I|I|

[that one guitar guy]

heres a basic, yet common blues prog. in C:
l C7 l F7 l C7 l C7 l
l F7 l F7 l C7 l C7 l
l G7 l F7 l C7l C7(G7)l
or with the minor 2 5 1 at the end
l C7 l F7 l C7 l C7 l
l F7 l F7 l C7 l C7 l
l D-7 l G7 l Cø7 l G7 l