Terry H asked: When a responder changes suit, it is forcing on opener to rebid. However what happens if opener’s rebid changes the suit again? Is this forcing on responder to bid again?
PG replied: It is normally forcing when a responder changes suit provided they are not a passed hand. It is normally not forcing when opener changes suit unless it is a jump bid or a reverse bid (where the new suit at the two level is higher ranked than opener's first suit and responder's bid was at the one level). So 1C - 1H - 1S would not be forcing, while 1C - 1S - 2H is a reverse bid and is normally forcing for at least one round.
Terry H also asked: What if opener’s bid is passed by responder, but opener rebids and changes the suit. Is this forcing on responder to bid?
PG responded: No it is not normally forcing unless opener bids the opponent's suit. However it does show a stronger or more distributional hand and so responder may now choose to bid to compete with the opponents.