Fourth Suit Forcing

Partner opened 1♣, you responded 1♥, and they rebid 1♠. You’re sitting there with 11 points, no three-card spade support, hearts that aren’t good enough to rebid, and you’re way too strong to pass. What now?

Enter Fourth Suit Forcing, one of the most useful bidding tools in your convention arsenal. It’s a get-out-of-jail-free card for awkward hands with game interest but no natural rebid.

What Is Fourth Suit Forcing?

Fourth Suit Forcing (FSF) is an artificial bid that asks opener for more information about their hand. When you bid the only unbid suit—the “fourth suit”—you’re not actually showing that suit. You might have one card in it, or none at all. Instead, you’re saying: “Partner, I have enough strength to invite or force to game, but I need your help finding our best contract.”

Think of it as a bidding tool, not a suit. You’re using the bid as a mechanism to gather critical information about:

• Whether opener has three-card support for your suit
• Whether opener has a stopper in the fourth suit (for notrump)
• Whether opener has extra length in either of their suits
• Whether opener has a minimum or maximum for their bidding so far

The beauty of Fourth Suit Forcing is that it keeps you from guessing. Instead of taking a stab at 2NT with no stopper, or rebidding a mediocre five-card suit, or raising partner on a doubleton, you have a systematic way to explore for the right game contract.

When Does Fourth Suit Forcing Apply?

Fourth Suit Forcing activates after a specific bidding pattern: both partners have bid two different suits naturally, and responder bids the only remaining suit at their second turn.

The pattern looks like this:

Opener bids suit A → Responder bids suit B → Opener bids suit C → Responder bids suit D

All four suits have now been mentioned, and that fourth suit by responder is the forcing bid.

Common Fourth Suit Forcing Sequences

Let’s look at the most frequent scenarios you’ll encounter:

1♣ - 1♥ - 1♠ - 2♦
Clubs, hearts, and spades have been bid naturally. Diamonds is the fourth suit and is forcing.

1♦ - 1♠ - 2♣ - 2♥
Diamonds, spades, and clubs have been bid. Hearts is the fourth suit.

1♣ - 1♦ - 1♥ - 1♠
Clubs, diamonds, and hearts have been bid. Spades is the fourth suit (at the one-level).

1♥ - 1♠ - 2♣ - 2♦
Hearts, spades, and clubs have been bid. Diamonds is the fourth suit.

1♠ - 2♣ - 2♦ - 2♥
Spades, clubs, and diamonds have been bid. Hearts is the fourth suit.

Notice that the fourth suit bid always happens at responder’s second turn. Opener has already shown their shape with two bids, and now responder needs additional information to place the contract intelligently.

What About Reverses?

Fourth Suit Forcing still applies even when opener has reversed (bid a higher-ranking suit at the two-level, showing 17+ points).

1♦ - 1♠ - 2♥ - 3♣
Even though opener has reversed and shown a strong hand, responder’s 3♣ bid is still Fourth Suit Forcing, asking for more description. The strength requirements shift (since you’re already in a forcing auction), but the asking nature remains.

What Should Opener Bid After Fourth Suit Forcing?

When your partner uses Fourth Suit Forcing, they’re essentially saying: “Tell me more about your hand.” You need to describe your distribution and strength more completely. Here’s your priority system for responding:

Priority #1: Show Three-Card Support for Responder’s Suit

This is your absolute top priority. If you have three cards in the suit responder bid first, raise it immediately. Most of the time, finding an eight-card major fit is responder’s main goal when using FSF.

Auction: 1♣ - 1♠ - 2♦ - 2♥ (FSF)

If you hold ♠K-Q-x ♥A-x ♦A-K-x-x-x ♣J-x-x, bid 2♠. You’ve found your 5-3 spade fit, and responder can place the contract from here.

With extra strength (15-16 points), you can jump to 3♠ to show three-card support with maximum values. This helps responder evaluate slam potential.

Priority #2: Bid Notrump With a Stopper in the Fourth Suit

If you don’t have three-card support for responder’s major, but you do have the fourth suit stopped, bid notrump. This indicates a balanced hand with values in the unbid suit, suggesting notrump as the best contract.

Auction: 1♦ - 1♠ - 2♣ - 2♥ (FSF)

With ♠x-x ♥K-J-x ♦A-Q-x-x-x ♣K-Q-x, bid 2NT. You’re showing a heart stopper and suggesting 2NT or 3NT as the final destination.

Your notrump bid level depends on your strength:

• 2NT = Minimum hand (12-14 points)
• 3NT = Maximum hand (15-17 points), taking a shot at game yourself

Priority #3: Rebid Your First Suit With Six+ Cards

If you opened with a six-card or longer suit, now’s the time to show that extra length. Rebidding your original suit tells partner you have significant extra length there.

Auction: 1♥ - 1♠ - 2♣ - 2♦ (FSF)

With ♠x-x ♥A-K-J-x-x-x ♦A-x ♣Q-x-x, bid 3♥. This shows six hearts and denies three spades or a diamond stopper. Partner now knows hearts might be the right trump suit even with only two-card support.

Priority #4: Show Four Cards in Your Second Suit

If you bid a minor at your second turn and actually have four cards in it (not just a convenient three-card suit), you can show that extra length.

Auction: 1♣ - 1♥ - 1♠ - 2♦ (FSF)

With ♠A-Q-J-x ♥x-x ♦K-x ♣A-K-x-x-x, you might bid 2♠ to show your four-card spade suit is real. Some pairs jump to 3♠ to show four good spades with extras.

Priority #5: Make the Cheapest Available Bid

If you can’t do any of the above—no three-card support, no stopper in the fourth suit, no six-card suit, no four-card second suit—make the cheapest possible bid. This is the “denial” response, showing a minimum hand with nothing extra to offer.

Auction: 1♦ - 1♥ - 1♠ - 2♣ (FSF)

With ♠A-Q-x-x ♥x-x ♦A-K-x-x-x ♣x-x, bid 2♦. This is the cheapest rebid available, showing you have a minimum opening with no help in clubs, no three hearts, and nothing extra anywhere.

After this “relay” bid, responder will place the contract based on their own hand.

Strength Requirements: Game Forcing vs. Invitational

Here’s where partnerships diverge significantly, and it’s critical you discuss this with your regular partner. Fourth Suit Forcing is not standardized across all bridge players.

Option 1: Game Invitational (10+ Points)

Many partnerships play Fourth Suit Forcing as invitational, showing about 10-11+ points. It doesn’t promise game, but it shows enough strength that game is possible if opener has extra values.

Under this agreement, responder might use FSF with hands like:

♠K-Q-x-x-x ♥A-J-x ♦x-x ♣Q-J-x (11 HCP)
After 1♣ - 1♠ - 2♦, you bid 2♥ (FSF) to see if partner has three spades or a heart stopper for notrump.

♠A-x-x-x ♥K-J-x-x-x ♦K-x ♣x-x (10 HCP)
After 1♣ - 1♥ - 1♠, you bid 2♦ (FSF) to check if partner has three hearts. With only 10 points, you’ll invite game if partner shows support.

This method gives you more flexibility with invitational hands but means the auction can stop below game if opener shows a minimum and responder has borderline values.

Option 2: Game Forcing (12+ Points)

Other partnerships, especially more experienced players, treat Fourth Suit Forcing as completely game forcing. Once you bid the fourth suit, the partnership is committed to reaching at least 3NT, 4♥, 4♠, 5♣, or 5♦.

With this agreement, you need about 12+ high-card points to use FSF. With 10-11 points and no clear rebid, you might need to:

• Rebid a five-card suit that isn’t quite robust enough
• Raise partner on a doubleton if it’s a minor
• Take a shot at 2NT without a perfect stopper
• Invite with 2NT and hope for the best

The advantage here is that once FSF is activated, both players can freely explore for the best game without fear of being passed out in a random two-level contract.

Which Method Is “Standard”?

There’s no universal standard. You’ll find strong players on both sides. The key is to agree with your partner and write it clearly on your convention card. Don’t assume—discuss it explicitly before you start playing together.

Fourth Suit Forcing: One-Round vs. Game Forcing

Adding another layer, some partnerships play a variation called “Fourth Suit Forcing for One Round” instead of game forcing through to game.

Game Forcing Fourth Suit

The auction cannot stop below game once the fourth suit is bid. Both players must continue bidding until reaching a game contract.

Auction: 1♣ - 1♠ - 2♦ - 2♥ (FSF, game forcing)

Now both players are committed to game. If opener bids 2♠ showing three-card support, responder cannot pass—they must continue to at least 4♠ or choose 3NT or another game.

One-Round Forcing Fourth Suit

The fourth suit bid forces opener to bid one more time, but after that, the auction can stop below game if responder makes a non-forcing rebid.

Auction: 1♣ - 1♠ - 2♦ - 2♥ (FSF, one-round forcing)

Opener must bid again (perhaps 2NT showing a heart stopper). Now responder can:

• Pass 2NT if playing it as invitational
• Bid 3♣ (non-forcing) suggesting clubs as a partscore
• Invite with 3NT if appropriate
• Force to game with other bids

This method provides more flexibility for invitational-strength hands but requires careful partnership understanding about which rebids are forcing and which are invitational.

Which Should You Play?

For newer partnerships, game forcing is simpler and clearer—once FSF is used, you’re going to game, period. For experienced partnerships with good judgment, one-round forcing offers more flexibility to stop at 2NT or three of a minor when appropriate.

Again, discuss and agree. Write it down. Stick to it.

When Is the Fourth Suit Natural?

This is a question many players ask: Can the fourth suit ever be a natural bid showing that suit?

The short answer: rarely, and only in specific situations.

After a Jump Shift

If responder made a jump shift (showing 17+ points and a strong hand), the fourth suit at their next turn is typically played as natural, not forcing.

Auction: 1♣ - 2♥ (jump shift) - 2♠ - 3♦

Here, 3♦ is natural, showing diamonds. Responder has already shown a powerhouse hand with the jump shift, so they don’t need an artificial asking bid to create a force.

At Very High Levels

Some advanced partnerships agree that fourth suit bids at the three-level in certain auctions (like 3♥ after 1♣ - 1♦ - 1♠ - 3♥) might be natural and show a real suit. But this is extremely rare and must be specifically discussed and agreed upon.

The Safe Default Rule

Unless you’ve explicitly discussed otherwise with your partner, treat the fourth suit as forcing and artificial in standard auctions. It’s much safer to assume it’s conventional than to pass partner’s Fourth Suit Forcing bid because you have three cards in the suit!

When in doubt, it’s forcing. Always.

Four Complete Example Auctions

Let’s walk through some full deals to see Fourth Suit Forcing in action from start to finish.

Example 1: Finding the 5-3 Major Fit

Opener: ♠K-Q-x-x ♥A-J-x ♦x-x ♣A-Q-x-x
Responder: ♠x-x ♥K-Q-x-x-x ♦A-K-x ♣J-x-x

Responder has 11 HCP and a five-card heart suit. After opener rebids 1♠, responder can’t rebid hearts (not good enough), can’t support spades (only two), and shouldn’t bid 1NT (too strong). So responder uses 2♦ (FSF) to ask if opener has three hearts. When opener shows 2♥, responder knows the 5-3 fit exists and jumps directly to game.

Example 2: Settling in Notrump

Opener: ♠A-x ♥K-x ♦K-Q-x-x-x ♣Q-J-x-x
Responder: ♠K-Q-x-x-x ♥A-Q-x ♦x-x ♣A-x-x

Opener shows a heart stopper by bidding 2NT. Responder, with no fit found but balanced distribution and game-forcing values, raises to 3NT. The heart stopper was crucial information—without it, responder might have had to try 5♣ or 5♦.

Example 3: Discovering Opener’s Six-Card Suit

Opener: ♠x-x ♥A-K-J-x-x-x ♦A-Q-x ♣x-x
Responder: ♠A-Q-x-x-x ♥x-x ♦K-x-x ♣K-Q-x

Opener rebids 3♥ to show six hearts. Responder, with two small hearts and enough values for game, raises to 4♥. The 6-2 fit plays better than 3NT here, especially with opener’s strong heart intermediates.

Example 4: Minimum Hand Relay

Opener: ♠A-Q-x-x ♥x-x ♦A-K-x-x-x ♣x-x
Responder: ♠K-x-x ♥A-Q-x-x ♦x-x ♣A-J-x-x

Opener’s 2♦ is the cheapest possible rebid, denying three hearts, a club stopper, or any extras. Responder, playing one-round forcing FSF, invites with 2NT. Opener, with a bare minimum 12-count and no club stopper, wisely passes. They might make 2NT, or they might not—but game is unlikely.

Common Fourth Suit Forcing Mistakes

Even experienced players make errors with Fourth Suit Forcing. Here are the most common mistakes and how to avoid them.

Mistake #1: Using FSF With a Natural Rebid Available

You hold: ♠K-Q-J-x-x-x ♥A-x ♦K-x-x ♣x-x

Auction: 1♣ - 1♠ - 2♦ - ?

Some players bid 2♥ (FSF) here, but that’s wrong. You have a perfectly natural rebid: 2♠, showing six spades. Don’t use Fourth Suit Forcing when you have a good natural bid available. Save FSF for hands where you truly have no clear descriptive action.

Mistake #2: Forgetting It’s Artificial and Passing

Opener holds: ♠A-x-x ♥K-Q-x ♦x-x ♣A-K-x-x-x

Auction: 1♣ - 1♠ - 2♣ (showing six clubs) - 2♥

Opener thinks: “Oh good, partner has hearts, I have three of them, let’s pass 2♥.”

WRONG! The 2♥ bid is Fourth Suit Forcing, not natural. Opener must bid again, and with three hearts, opener should bid 3♥ (or 2♠ if that’s cheaper) to show support. Passing a Fourth Suit Forcing bid is a disaster—you might have a cold game while sitting in a 5-1 or 6-1 heart fit at the two-level.

Mistake #3: Using FSF on Minimum Hands

You hold: ♠Q-x-x-x-x ♥K-x ♦J-x-x ♣K-x-x (8 HCP)

Auction: 1♦ - 1♠ - 2♣ - ?

If you’re playing FSF as invitational (10+) or game forcing (12+), you cannot use it here. You don’t have the strength. You’ll have to bid 2♦ (preference) or pass 2♣ if you can tolerate it. Fourth Suit Forcing promises values—don’t use it just because you’re searching for a bid.

Mistake #4: Opener Not Following Priority System

Opener holds: ♠K-x-x ♥x-x ♦A-K-Q-x-x ♣A-x-x

Auction: 1♦ - 1♠ - 2♦ (showing six diamonds) - 2♥ (FSF) - ?

Some openers bid 2NT here, eager to show values. But wait—you have three spades! The correct bid is 2♠, showing three-card support. Don’t jump to notrump when you have the fit responder is looking for.

Mistake #5: Responder Not Planning Ahead

You hold: ♠A-Q-x-x-x ♥x-x ♦x-x-x ♣A-Q-x (11 HCP)

Auction: 1♥ - 1♠ - 2♣ - ?

You want to use 2♦ (FSF), but ask yourself: “What am I planning to do after partner’s response?” If partner bids 2♥ (showing six hearts), what’s your plan? If partner bids 2NT (showing a diamond stopper), can you pass or do you need to bid again?

Always have a plan for common responses before using Fourth Suit Forcing. Don’t use it as a general stall tactic.

Mistake #6: Forgetting Partnership Agreement

You and partner haven’t discussed FSF.

This is the biggest mistake of all. You think it’s game forcing. Partner thinks it’s invitational. You think it applies at the three-level. Partner thinks it’s only at the two-level. Disaster ensues.

Before using Fourth Suit Forcing, make sure you and your partner have agreed on:

• Game forcing or invitational?
• What’s the minimum strength?
• Does it apply at all levels?
• Opener’s priority system
• One-round forcing or forcing to game?

Write it on your convention card and discuss it explicitly.

Why Fourth Suit Forcing Belongs in Your System

Fourth Suit Forcing solves one of bridge’s most frustrating problems: what do you bid with game-invitational values but no natural rebid?

Before FSF existed, players would:

• Rebid mediocre five-card suits and miss 5-3 fits elsewhere
• Raise partner on a doubleton and play in a 7-card fit
• Blast into 3NT without stoppers and go down when a suit runs
• Pass and miss cold games with 25-26 combined points

Fourth Suit Forcing gives you a systematic, intelligent tool to handle these awkward hands. It earns its place at the table every single session. Once you and your partner start using it consistently, you’ll wonder how you ever bid accurately without it.

Final Thoughts: Make It Part of Your Partnership

Fourth Suit Forcing is not optional for serious players—it’s essential. It’s one of the fundamental conventions that separates competent pairs from struggling ones.

The key to success with FSF is threefold:

1. Agreement: Discuss every aspect with your partner and write it on your card
2. Priority: Opener must follow the priority system rigorously (support first!)
3. Judgment: Responder must use it only when appropriate, not as a panic button

Take the time to learn it properly, practice it with your regular partner, and make it a automatic part of your bidding system. Your game results will improve, your partnership confidence will grow, and those awkward 11-point hands will suddenly have a clear, forcing path to finding the right game contract.

Remember the golden rule: When in doubt, the fourth suit is forcing. Always.