Fourth Suit Forcing
In my partnerships I prefer to call it fourth suit game forcing. It is much more simple to play it as game forcing, to eliminate any misunderstandings or subsequent bidding issues that may arise.
So, the key characteristics are:
A) It is game forcing
B) It applies after three suits have been bid naturally.
Fourth suit sets up a game force, and asks your partner to give more information about their hand.
In this hand you would like to know more information about your partner's hand. Do we have a diamond stopper for No Trump? We could have a fit if partner has six hearts or a five clubs. It is also very possible that partner has three spades.
Expert hint: In the above auction many experts play a bid of 2♠ by north to show two cards, and a bid of 3♠ to show three. So, this below auction would likely show a 3514 shape hand. It is not particularly important to play it that way, some people prefer playing a simple 2 ♠ as showing three cards (delayed support). It is a matter of partnership agreement, as always it is more important to be on the same page as your partner than to be "correct".
Now that we know how fourth suit applies, let's consider our options other than 4th suit.
Expert hint: To keep it simple, many expert partnerships have the following rule "If 4th suit is available, it is the only way to game force. Anything else is not game forcing".
With the above rule in mind, consider this auction.
What would the following bids mean
3D = ?
3S = ?
3H = ?
2NT = ?
Since the rule says our only way to game force in this auction is to bid fourth suit 2 ♣ , anything else is not game forcing. Those bids are therefore natural invitational bids. It has a big advantage of being simple and clear.
This is a possible continuation
South started by looking for a major fit in hearts, when one was not found, she invited in diamonds.
The next article on fourth suit forcing will cover the responses in more detail. You will notice that the bids are mostly very intuitive and natural.