I’ve mentioned before that the blues is the basis for more jazz songs than any other form. On a very basic level, “the blues” to me means a progression of: tonic, subdominant, [tonic], dominant, tonic. This may not seem like a Bb blues at first listen, but on closer inspection it has some telltale characteristics. The melody starts by roughly describing a Bb7 tonality, then goes through E to Eb. We move into a more obscure area until the altered C# chord, which is right where we’d normally find a G7. Then it cycles through C and F back to Bb.