Hi - The only dumb question is a question not asked right?? please keep this in mind for the duration of this post Going through the first module of the walking basslines Triad Modules book. You say the example will be applied to a 12-bar blues in F. Here's the question: Typical 12-bar blues is a I-IV-V progression, however your examples present an additional chord, the D (F, Bb, Cm, D). What is the purpose for this and why did you deviate from a traditional I-IV-V? I get it for the turn around..but not in the 8th measure replacing the one. thanks!