4th Suit Forcing (4SF)

by Steve Turner1

Premise:   A way for responder to create a forcing auction, at the 2nd turn to bid, when no natural sequence exists to do so (for example, jump rebids by responder either in opener's 1st bid suit or in responder's 1st bid suit are invitational (i.e., NOT FORCING), thereby creating the need to generate a sequence which IS forcing to opener). The treatment about to be discussed bears a strong resemblance to "New Minor", with some very important differences.

A typical "4th suit forcing" format is the following:  1C-1H-1S-2D or 1D-1S-2C-2H, where the 4th suit is artifical, at least invitational, requesting descriptive "prioritized" rebids from opener:
  1. simple raise of responder's 1st bid suit with 3-card support and a minimum.
  2. jump raise of responder's 1st bid suit with 3-card support and a maximum.
  3. 2NT with the 4th suit stopped, lacking either of the above, likely doubleton w/opener's 1st bid suit, but a singleton sometimes.
  4. raise the 4th suit with 4-card support.
  5. make the most natural rebid possible, lacking any of the above.

Opener's Response to the Fourth Suit

First, some example hands will demonstrate how opener responds to a 4th suit sequence by responder. Each example below shows opener's hand, starting the auction with 1C (except d: 1D).

S KJxx
H Jxx
D xx
C AKxx
S AKxx
H Qxx
D xx
C AJxx
S AQxx
H xx
D Kxx
C K10xx
S KJxx
H x
D KQ10x
C Axxx
Answer: 2H Answer: 3H Answer: 2NT Answer: 3C

e) f)
S KJxx
H Axxx
D x
C KQ10x
S AQxx
H xx
D x
C AKxxxx
S Kxxx
H xx
D Jx
H Jx
D xx
C AQxxx
1C-1D-1H-1S-? 1C-1H-1S-2D-?
Answer: 2S or 3S Answer: 3C Answer: 3C Answer: 2H,2S,3C

S Qxxx
D xxx
C AJxx
S KQxx
H Qx
D Jxx
S AJ10x
C 10xxxx
Answer: 2H Answer: 2NT Answer: 2NT

Variations in Agreements

Std version of 4SF Game force (4SFG)
Hardy version of 4SF Game force, unless responder rebids the 4th suit (always lower ranking and constructive to invitational, roughly 8+ to 11)
Mod version of 4SF A rebid of 2NT by either opener or responder can be passed and the Hardy version rule applies as well

If you agree to use the Std version, ALL rebids after 4SF are game forcing. No exceptions. Therefore, you need to discuss this treatment (used by many partnerships) if you agree to 4SFG.

If you agree to the Hardy version, the following type of auction in non-forcing:  1C-1H-1S-2D-2NT-3D (typically x AJ10xx KJxxxx x). Had responder held 6 hearts and 5 diamonds instead, same strength, a 2H rebid is more reasonable (instead of 4th suit), almost always promising a 6-card suit, non-forcing.

If you agree to the Mod version, the following type of auction can occur:  1C-1H-1S-2D-2NT-P... This allows for invitational misfits. If responder picks up, for example:  SQx HA10xxx Dxxx  CKQx , wouldn't it be nice to stop in 2NT? Does responder have any intelligent choice other than 4SF (2D) after opener's rebid? Opener could easily have any one of several hands that should play in no higher than 2NT.  Refer to hands c), j) and k), above.

Responder's Use of Fourth Suit with Strong Hands

Now for some responder hands, after a 1C opening, followed by a rebid of 1S:

S Kx
D xx
C KJxxx
S KJxx
H AQ10xx
D x
S x
H KQJxxx
C Jxx

With a), does responder have a bid other then 4SF (2D) at the next turn to bid? Responders rebid of 3C, after opener rebids, shows a game force with good club support. Remember, any suit bid by responder at the 3-level, following 4SF, is still forcing, EXCEPT a rebid of the 4th suit.

With b), the hand is too good to jump to 4S at responder's 2nd turn to bid. Slam is a strong possibility, so it's time to explore. Voila - 4SF, followed by a raise later. Opener will know that we have a slam try here (since responder neither invited (jump to 3S) nor jumped to game directly). The 4SF temporizing bid, followed by a raise, shows this type of hand.

With c), responder uses 4SF, followed by hearts (showing 6 and a game force). Very descriptive and allows for co-operation from opener to find the best spot.


When considering a gadget, given a choice between it and another, the decision usually gets down to frequency of occurrence.

There is very little doubt that 4SF is superior to the old-time standard methods, due to the non-guesswork to land on your feet, with little cost on the majority of hands. The real decision (and perhaps the jury is still out on frequency) is "which treatment" of 4SF to adopt.

Caveat for 2/1 System bidders:

The auction 1(minor)-1H-1S-3(other minor) describes a hand which contains a very good 6-card suit and 4 of the major, invitational strength. Does this treatment sound familiar? The "new minor" variation is similar, 'tho the hand strength range promises the upper end with the 4th suit approach. With "new minor", opener's hand promised to be balanced with a 1NT rebid; therefore, a jump to 3 of the other minor after a 1NT rebid can be made on lesser values and some latitude on suit strength. The partnership is guaranteed at least an 8-card fit in the new minor, and safety is more likely. Thus, without a 1NT rebid, and a distributional misfit a possibility, a strong suit and invitational values is a sensible requirement. 

This auction does not really apply to SAYC bidders, since the other minor (1D-2C or 1C-1D) can be bid immediately (unless you have a strict agreement that responder must bid a 4-card major instead of a 6-card minor with less than game values - if you do, you might consider the alternative approach).

1See the following primary reference for more information.

Max Hardy (1989) Two Over One Game Force. Published by Max Hardy, Las Vegas, Nevada.