Originally Posted by: zreynoldsp
I've substituted add9 chords in standard progressions before, and that works well for a different sound...

Correctomundo.

I play allot of blues and blues based stuff and what I have found (IMO) is that the 7ths are used mostly for the slower songs or songs that require chord fills. The 7th lends itself easily to use your finger more within the pentatonic scale position.

ALA Jimi--Little Wing, SRV--Couldn't stand the weather, Los Lonely Boys -- How far from Heaven Main Rhtyhm(actual chords are G and AM) are some good examples.


9ths tend to be played more for up tempo songs since the finger groupings are closer together and as you have noticed can be played easier.

You may also notice that the 9th is used more in the "turnaround" of the blues progression.

I also read somewhere that different blues genres--Delta, Chicago, Memphis, Texas Blues are sometimes classified by the chords they use and if memory serves me correctly the 9ths were commonly used more in the chicago style?

Your question was when is the correct time to use which one? I am more inline with ZRP had to say -- Whatever sounds good. Blues is like jazz -- Music of the Moment. If it sounds good don't worry to much about why, just........go with it.