Fourth suit forcing is a contract bridge convention that allows responder to create, at his second turn to bid, a forcing

Forcing bid

In the card game contract bridge, a forcing bid is any bid that obliges the partner to bid over an intermediate opposing pass. Owing to the partnership's bidding system or a bridge convention, partner must "keep the bidding open", i.e...

 auction. A bid by responder in the fourth suit, the only remaining unbid suit, is artificial indicating that responder has no appropriate alternate bid, remains interested in the potential for a game contract and asks opener to bid again to show additional features.

Opener responds to the fourth suit forcing by (in prioritised order):

1. Raising of responder's first bid suit with 3-card support,
2. Bidding notrump with values in the fourth suit,
3. Raising the fourth suit with four cards in that suit,
4. Making the most natural rebid possible, lacking any of the above.

Fourth suit forcing is minimally forcing for one round and usually forcing to game - partnership agreement is required. Whether or not the convention is applicable if the fourth-suit bidder is a passed hand is also a matter of partnership agreement; there is no consensus amongst experts on the options as to its use being non-forcing, forcing, or forcing only after a reverse.

The convention was introduced by the British bridge author Norman Squire and is adopted by the majority of partnerships playing at competitive levels. Useful with strong game-going hands where responder has no natural forcing rebid, it is a type of game trial bid.

Example 1

North	South
1	1
2	?

South holds in the auction at right.

After 2 by North, South sees there is likelihood for game given that the partnership has bid three suits bid and holds around 24-26 high card points. However, he does not have a good natural bid available; each would give partner the impression of stronger support than he has, and might lead to a poor choice of contract.

• He has shown his spade suit fully. To rebid spades would imply a longer or stronger suit than he has; they are not good enough for a 3 rebid.
• He cannot bid in support of either minor suit because his holding in both is inadequate.
• He cannot bid notrumps because it implies a heart stopper, which he lacks and his partner is quite likely to lack as well, having shown two suits so far. If he bids notrumps and ends up in 3NT, a heart lead will be an obvious strategy and loss of four or five heart tricks is possible.

South instead bids the fourth suit (fourth suit forcing), i.e. 2, to indicate that he believes they have values for game, that he lacks a stopper in hearts needed for notrumps and that he has no viable bid in any of the other suits. Depending on partnership agreement, this 2 bid may be either forcing

Forcing bid

In the card game contract bridge, a forcing bid is any bid that obliges the partner to bid over an intermediate opposing pass. Owing to the partnership's bidding system or a bridge convention, partner must "keep the bidding open", i.e...

 for one round, or forcing to game.

Example 2

North	South
1	1
1	2
2	2

The fourth suit forcing approach in conjunction with the principle of fast arrival

Principle of fast arrival

In the game of contract bridge the Principle of fast arrival is a bidding treatment widely used in game forcing auctions whereby:* Bidding game directly, usually a jump bid, shows a minimum hand for your previous bidding, and is limiting, and...

 allows the partnership to create a game-forcing

Forcing bid

In the card game contract bridge, a forcing bid is any bid that obliges the partner to bid over an intermediate opposing pass. Owing to the partnership's bidding system or a bridge convention, partner must "keep the bidding open", i.e...

auction at low level that leaves ample room to explore for slam.

Here, the 2 bid denotes a four card spade support, and a hand too strong for a fast-arrival bid of 4.