~Fourth Suit Forcing

Fourth Suit Forcing (FSF)

In a noncompetitive auction, when three suits have been bid, responder may want to make the auction forcing and may do so by bidding the fourth suit no matter what that suit holding may be. Some partnerships play FSF as game forcing; others play it as a one-round force.  If opener has a sound opening bid, he knows from the FSF bid that game should be reached if a reasonable fit can be found.
~Opener’s first responsibility is to show 3-card support for responder’s major suit. Holding 3-card support, opener either rejects the game invite by bidding 2 of the major or accepts the invite with 14+ HCP by jumping to three of the major.
~When opener does not have 3-card support for responder’s major, the second priority is to bid notrump with a stopper in the fourth suit. With minimum values of 12-13 HCP, opener rejects the game invite by bidding 2NT. With greater values, opener must accept the invite and jump to 3NT.
~Priority three: when opener can neither show a 3-card fit nor bid notrump, he makes the most descriptive bid possible. Opener may rebid his first suit with 5 cards in the suit or support the fourth suit with 4-card support.

Opener can have one hand that cannot be described; holding four cards in each of the two suits bid and no stopper in the fourth suit, opener rebids the second suit, implying 7-5 shape (with 6 cards in a minor and 5 cards in a major, opener would open the major). Responder should realize that opener may be stuck for a bid and should allow room for opener to further describe the hand.

Another hand presents a potential problem. That problem is to assign a meaning to the 1S bid in the sequence 1C-P-1D-P, 1H-P-1S–is the 1S fourth suit forcing and what would a 1NT, a 2S, and a 2NT or 3NT bid mean? My recommendation:
~1S: is a one-round force showing a 4-card suit. You are still looking for a trump fit. The hand might hold 6-9 HCP but could be stronger.
~1NT: shows 6-10 HCP and a spade stopper (or half stopper) but less than four spades–not forcing.
~2S: 10+ points without a spade stopper and no 4-card spade suit. If you had a 4-card spade suit, you would bid a forcing 1S.
~2NT: 11-12 HCP and a spade stopper–invitational.
~3NT: 13+ HCP and a spade stopper.

Responder could have the values for a game force or a slam invite. If none of the four bids shown are forcing, there must be a forcing bid. Hence, 1S is forcing for one round but may not contain invitational values. To make a FSF (2S or 2NT), responder must hold invitational or game-going values and shape for at least an invitational bid opposite a minimum opener.