FelicityR, on 2017-April-30, 01:28, said:
but (as far as I am aware, please correct me if i'm wrong) there is only one scenario where the 4th suit is not forcing to game: the auction 1♣ - 1♦ - 1♥ - 1♠, and on this occasion the 1♠ bid is an actual suit.
I can think of some other scenarios depending on the conventions one plays.
Playing short club openings, there is no FSF possible when the auction opens 1
♣ and there is ANY response at 1-level, because 2
♣ is always available as a "new" suit: so not only is your example above true, but 1
♣ - 1
♦ - 1
♥ - 2
♣ is equally forcing one time and denies an actual suit of spades.
Playing 2/1 as unconditionally game forcing, I wouldn't call the fourth suit (as in question 3 above) FSF, as the game force was already in place and implications like fast arrivals may be different and remain in place.
Plus of course playing XYZ or similar a 2
♣ or 2
♦ fourth suit may have a meaning defined by the convention.