Fourth Suit Forcing is a very useful convention which can be used as a one-round force or Game Force. I prefer to use it as Game Force. When 3 suits have been bid and you are "above" the one level, a fourth suit mentioned in the auction may be "artificial" and is forcing. Since the 4th suit mentioned here is not a true suit -- partner MUST have a stopper in that suit to bid NOTRUMP.

Whether you play 4th suit forcing to game or one round, responder is asking opener to further describe his hand. If the partnership is playing this Convention as a one-round force, responder would have to jump on his rebid to force to game..

Partner

Hand 1

	A5 765 KQ765 A76

	KJT86 KQ9 A JT32

North	East	South	West
-	Pass	1S	Pass
2D	Pass	3C	Pass
3H*	Pass	3nt	Pass
Pass	Pass	Pass	-

South opens 1S. North knows that they have game values but is uncertain as to where to place the contract.

The 3H bid by responder is Fourth Suit Forcing. Since it is the fourth suit bid during this auction it says nothing about Hearts.

The full meaning of the bid will be clarified on responder's next bid. With a Heart Stopper South bids 2nt and North goes to Game.

Partner

Hand 2

	96 Q2 AK32 AQJ43

	AQJ74 87 QJ87 KT

North	East	South	West
---	Pass	1S	Pass
2C	Pass	2D	Pass
2H*	Pass	2nt	Pass
3nt	Pass	Pass	Pass

South opens 1S. North knows that they have game values but is uncertain as to where to place the contract.

The 2H bid by responder is Fourth Suit Forcing here and says nothing about Hearts. With a Heart Stopper South bids 2nt and North goes to Game.

References: Pattaya Bridge Club Reference