3rd Suit Forcing

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When opener's 2nd bid limits their hand, responder becomes the Captain of the Auction, responsible for guiding the auction to the right contract.  Responder's goal may be to:

1. play a partscore
2. invite game
3. force to game
4. make a slam try
5. choose the right strain
   1. look for support for their major
   2. assess whether notrump is viable
   3. try to right-side a notrump contract
   4. sometimes look for a fit in the other major

When opener rebids their minor at the 2-level, they are showing a 12-14 HCP hand with a 6-card minor.  

On the above auction, does South's jump to 3♠ show an invitational hand like ♠AKJ864 ♥K84 ♦72 ♣94
or a game forcing hand like ♠AKJ864 ♥AK4 ♦72 ♣94?

How would you bid the other hand?

There is not enough room for natural bids to show responder's distribution and strength.   

The uncontested 1m-1M-1NT auction is analogous.  Responder needs ways to signoff, invite, and force.  Many partnerships use a conventional New Minor Forcing bid to allow responder to show a wide variety of hands and gather the information they need to place the contract.  2-Way New Minor Forcing is easier and better.  It uses 2 conventional bids to help responder find the right contract.

When opener rebids their minor, responder has similar needs.  We recommend using the cheapest unbid suit as an artificial game force.  This agreement is called 3rd Suit Forcing.  It allows responder to clearly differentiate responder's invitational hands from game forcing hands.  Using the cheapest unbid suit as an artificial game force make the bid alertable.  Using the cheapest unbid suit to establish a game force leaves room to choose the best game.  (See our Game Priorities article.)

Playing 3rd Suit Forcing,any bid below game, other than the 3rd Suit Forcing artificial game force, is invitational.  Since 2 of opener's long minor is a viable contract, responder can pass with a less than invitational hand.  So responder's jump to 3♠ is highly invitational, showing a 6-card or longer spade suit, e.g. ♠AKJ864 ♥K84 ♦72 ♣94.

Responder would use 3rd Suit Forcing to establish a game force with a game forcing hand, e.g. ♠AKJ864 ♥AK4 ♦72 ♣94.

Here is a summary of responder's options after opener's 2m rebid playing 3rd Suit Forcing

After responder's invitational raise, opener with a minimum may pass if the contract is viable.  If the contract isn't viable, a minimum opener will suggest stopping in a different partscore, typically 2NT or 3 of their minor.  

If opener is closer to a maximum (14 points, or a good 13), they will bid game or make a move towards game by showing 3-card support for opener's major or showing a stopper in a side-suit to help assess whether 3NT is viable.  Responder, the Captain of the Auction, will look for the right game.  As discussed in our Game Priorities article, a minor suit game is the game of last resort because it requires 11 tricks and earns just 20 points per trick. 

Here is a summary of opener's continuations after responder's 3rd Suit Forcing artificial game force.

After responder's 3rd Suit Forcing artificial game force, opener describes their hand to help responder choose the right game using the priorities discussed in our Game Priorities article. Opener will prioritize showing 3-card support for opener's major to help assess whether a major suit game is viable, or showing a stopper in a side-suit to help assess whether 3NT is viable.  Opener shouldn't make a jump bid.  Responder became the Captain of the Auction when opener limited their hand by rebidding their minor.  Opener should leave room for responder to find the right game or make a slam try.