Diminished / half diminished

Greatape

RelayDuzzy said:

kelpbeds said:

More amusement, play m7b5 arpeggios from the major third of a dominant 7th chord to create a dominant 9 sound. Great in a Blues context. 

I was just going to ask about how to use it. I've just been learning about m7b5 chords, and after some messing around noticed that they were spelt the same as dominant 9 chords.  So the question is when it sounds right, how do you know over any given chord, whther you're playing a m7b5 or a dominant 9th chord?

'Is it a m7b5 or a 9th chord? Yes'

Handy perhaps to conceive of C9 as Em7b5/C in some circumstances. 

And then go all James Brown and just play a Gm triad on the top strings.