Substituting all chords with relative minor/major...?

Question

I was mucking around with Oasis' "Don't look back in anger" on the acoustic guitar/vocals.

I was using these chords, but on capo 4 as I reworked the song a bit: http://tabs.ultimate-guitar.com/tabs/o/oasis/dont_look_back_in_anger_acoustic_ver2_crd.htm

For fun, I tried substituting all the chords with their relative major/minor versions e.g. C<-->Am, G<-->Em, F<-->Dm (wasn't sure what to do with E7). It sounded pretty cool.

I wondered if this is something that has a name... what am I actually doing from a music theory perspective? Or, am I just writing a completely new song?

Answer 1

Your are just substituting the chord for a related one there's really not much else going on. It's very common especially in jazz to take a similarly functioning chord and substitute it in to give the progression a slightly different flavor.

Also asumming the 5th is always in the melody and you are actually just adding an extention the 13th or 6th depending in how you want to look at it. So your actual progression would be C6 - G6 - F6.