Other Preempts
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.
Many partnerships also use Michaels Cue Bids preemptively. A Michaels Cue Bid is a bid of two of a suit in which an opponent has bid one that promises two five-card suits including the unbid majors and, in most partnerships, at least seven or eight HCP. Thus, either 1♣-2♣ or 1♦-2♦ promises both five hearts and five spades, 1♥-2♥ promises five spades and either five clubs or five diamonds, and 1♠-2♠ promises five hearts and either five clubs or five diamonds. Over a Michaels Cue Bid in either major suit, partner's response of 2NT asks the Micheals bidder to bid the minor suit. If the Michaels bidder has a strong hand, the Michaels bidder can show the strength by rebidding an agreed suit at a higher level.
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