I've recently begun writing a blues song in the muddy waters sort of style, and, throughout i make a lot of reference to previous blues songs (Got My Mojo Workin', Hoochie Coochie Man and Crossroads being examples). Now, I was wondering if this is against copyright, I don't actually take any lyrics from any of the songs, just mention them by their titles, and I've heard it done in other works, but is there some kind of special permission that must be received?