Fourth suit forcing is part of what teachers refer to as “Responder’s second bid”. This is a conventional bid and is therefore only used in the absence of a satisfactory natural bid. But unlike many conventions, it is essential. Here is a simple yet comprehensive summary. To be read and reread.
1. What conditions must be met to use fourth suit forcing?
The use of fourth suit forcing implies that three suits have already been bid, which eliminates all sequences where Opener bids No-Trumps or repeats his suit. In our study, Responder’s first bid will always be a new suit at the 1-level, therefore never a 2-over-1 new suit. This study does not look at strong rebids by Opener (reverse or jump shift) either. The sequences you will work on therefore involve the use of fourth suit forcing after a non-reverse, 1♥-1♠-2♣, and after an ambiguous rebid, 1♣-1♦-1♠. The main role of fourth suit forcing is to ask for additional information about Opener’s hand. It guarantees a minimum of 11 HCP so as not to find yourself too weak for the level that will be reached on the third round of bidding. It must only be used in the absence of a satisfactory natural bid.
As the name suggests, it is forcing, therefore Opener is obliged to respond, but it is also auto-forcing, which means that Responder promises a third bid (unless Opener jumps to game). However, fourth suit forcing is not game-forcing. You must stop when, and only when, Responder has 11 HCP exactly opposite a minimum opening.
Note: When Responder must bid a reverse or go to the 3-level to bid the fourth suit, the bid becomes game-forcing.
Three possible sequences:
2. When should you use fourth suit forcing?
To understand how useful it is, let us start by recalling the non-forcing nature of several Responder’s second bids.