Laws of Blues Harmonica - 3 Draw Rule (Relative to Chords)
If the 3 draw B (or 3 draw quarter tone bend as discusses yesterday) is an emphasized note in your first lick of the 12 Bar Blues progression, and you wish to continue the chorus with that lick as a theme (think Chorus Forms as taught in the Improvising Studies), then when the lick is repeated over the IV7 Chord you should bend the 3 draw down to 3' Bb and 3" A over the V Chord.
Here's the basic theory...
I7 = G B D F (referencing C Harmonica in 2nd Position, Key of G) and 3 B is the 3rd of the chord.
IV7 = C E G Bb and B does not match, but 3' Bb does... it's the flat-7th of the chord.
V7 = D F# A C and again B does no match, but A does... it's the 5th of the chord.
So, the simple rule is...
I7 = 3
IV7 = 3'
V7 = 3''
Not only does it sound very cool to change your main lick in this manner over the chord changes, it sound pretty bad when this rule is not followed. intermediate (and commonly advanced) players working on their improvising make this mistake all the time. Now that you know, you won't :-)
Have a great weekend everyone!