I to IV are so if'fy. Cmaj7 to Fmaj7 progression. (America type tunes) Don't know what to do until the next chord. C and F, the same problem. IV chords are the suspensions of the major key setup. Play an F with G in the bass (F/G), we have the ultimate suspension. Aurally, we make an assumption. This can go anywhere. IV chords are ambiguous. Why the early hatred of tritones?