In the blues tune by Rush, Here Again, it opens with, I believe, a Bm, A7, E7 progression. Then in the verse it is Bm, E7, A7. I, IV, V tells me this is in the key of Em. Is this correct? And if so, is it common to start a progression on the V chord? I'm about half way through the Blues level 1, so this may be addressed later. Or, maybe it was mentioned earlier and I missed it. Thanks for any help.