Topic: Substituting chords.

How do you go about working out what chords you can use as a substitute chord? I'd like to be able to throw something different into the mix when i'm strumming away on chord progressions. Instead of playin 2 whole bars of E for example I like to throw an E7 in every 2nd beat or so just to change things slightly.
I know how to work it out for major chords, instead of C you could throw in a Cmaj7 or a Cadd9 or something, because these are derived from the major scale, just adding a note to a triad. But how do you go about working out what chords you can use in place of say an F#m or a D#dim?
Does anyone know the theory I should be looking at here?

I'm pretty much stumped on this one, so any help would be greatly appreciated.


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Re: Substituting chords.

Probably the simplest rules for substitution sits around Dom7 chords.  You can substitute in any extended 7th and be just fine, and vice versa.  You can play a 9, 11, or 13 as well, and you can go the other way, too.

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