a couple of other notes: the IV7 chord is perhaps the most important in changing a folk harmony into a blues harmony (mentioned in my post above as A7 in E). I7 and V7 are also important, but both are freely used in other folk--and pop--forms without providing a bluesy sound.

There are also some classic blues turnarounds, like /I-I7-IV-IVminor/I-V7- - / and /I-IIdim-IIbdim/Idim/I-V7- - /.

-seed