Preempt
Preempt (also spelled "Pre-empt") is a bid in contract bridge whose primary function is to take up bidding space from the opponents. A preemptive bid is usually made by jumping, i.e. skipping one or more bidding levels. Since it deprives the opponents of the bidding space, it is expected that they will either find a wrong contract (too high or in a wrong denomination) of their own, or fail to find any.
Preempting is often made with the aim of a sacrifice, where a partnership bids a contract knowing it cannot be made, but assumes that (even when doubled), the penalty will still be smaller than the value of opponents' bid and made contract.
A preemptive opening bid is an opening bid on level 2 or higher, typically made with a weak hand containing a long, strong suit. Preemptive opening bids on level 3 and higher are common for most bidding systems in the world. For example, the hand of ♠4 ♥KQJ9854; ♦J62 ♣ 95 is a typical 3♥ opener. The bid is made on presumption that, without any additional tricks from the partner, at least 6 tricks can be taken with hearts as trump, and the potential penalty of 500 points in 3♥ doubled is smaller than the value or opponents' likely game or slam (cca. 600 and 1400 points respectively).
A partnership can preempt the opponents cooperatively, having discovered that they have an excellent suit fit but not much overall defensive strength. For example, after the partner opens 1♦ and RHO doubles, the following hand is suitable for a bid of 5♦, outbidding opponents' major suit game in advance:
♠83 ♥4 ♦Q108542 ♣QJ64
In a more general sense, even low-level and non-jump bids can have a preemptive value if they deprive the opponents of bidding suits that they could otherwise bid on level 1 or 2. For example, weak 1 notrump (characteristic for Acol system) opening takes up entire level 1 from the opponents, who could bid their long suit on level 1 had the opening been 1 of a minor, like in Standard American bidding. However, there is always the danger that the preempting side could preempt themselves, taking up their own bidding space that could be used for constructive bidding. For example, four-card major openings have a more preemptive effect compared with five-card major openings, but also carry less precise information, as the partner should not support the opened suit without at least 4 cards; that could result in missing a partial contract or even a game.
