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Calls made during the auction phase of a contract bridge game convey information about the player's card holdings. Calls may be "natural" (that is, are based on a holding of the suit bid, or a balanced distribution in the case of a notrump bid) or "artificial" (show a feature unrelated to the named denomination). A bridge convention is an agreement about an artificial call or a set of related artificial calls. Contract bridge is a trick-taking card game played by four players in two competing partnerships in which a sequence of bidding, also known as the auction, precedes the play of the cards. The purpose of this bidding is for players to inform their partners of the content of their hand and to arrive at a suitable contract at which to play the hand (or to prevent the opponents from arriving at a suitable contract). Although bidding is often "natural" (describing a hand by simple reference to possession, shape, and strength of the named suit) players may also bid using conventions, which assign more specific information to certain calls, particularly at the more advanced levels of competitive play. Bill Root defines "convention" as, "A specific agreement between partners to give an unusual meaning to a bid". However, some conventions, for example, Stayman, are very widely used and cannot be said to be unusual. Conventions are often named after their ostensive author (the Drury convention), their promulgator (the Stayman convention), or something about the methodology itself (the strong two clubs convention). The term ''conventional'' is also used to describe certain opening leads, discards and signals that have specific agreed meanings. Conventions to be played must be agreed by partners before play begins and must be disclosed to their opponents, either in advance by the use of or by alerts, announcements, and answers to questions about one's partner's bids once bidding has begun. Generally, this disclosure also must include the negative implications of choosing the bid over another alternative. Failure to reveal fully the existence and meaning of a convention generally constitutes an illegal communication of information between partners. Perhaps the most widely known and used conventions are Blackwood, which asks for and gives information about the number of aces and kings held, Stayman convention, used to discover a 4-4 fit in a major suit following an opening no trump bid, Jacoby transfers, used to find a 5-3 fit in a major suit, and strong two clubs to show a very strong hand (usually at least 22 HCP). It could be argued that takeout doubles are conventional but their usage is so widespread that they may be considered a natural call. ==Classification== Bridge conventions can be classified according to their purpose: *Opening bid conventions * *Strong opening bids are used for hands stronger than the "normal" opening bid range (12-20 points in natural systems, 12-15/17 points in artificial systems) * * *Strong two clubs in natural systems denote hands of 22+ high card points * * *Strong one club in strong club systems denotes hands of 16-17+ points * *Weak opening bids are used for hands weaker than the normal opening bid range, but with preemptive value: * * *Standard preemptive bids, including "weak two" Bids * * *Kamikaze 1NT * * *Ekren * * *Muiderberg * *Other opening bid conventions: * * *Flannery * * *Multi 2 diamonds * * *Namyats *Fit-seeking conventions are used in constructive bidding, in order to find a fit—a suit suitable to be a trump suit * *Baron * *Checkback Stayman * *Forcing notrump * *Jacoby transfers * *New minor forcing * *Stayman * *LTC *Slam-seeking conventions are used in constructive bidding to investigate the possibility of a slam contract (''Main article: Slam seeking conventions'') * *Asking bids * *Blackwood * *Cue bids * *Gerber * *Grand slam force * *Jacoby 2NT * *Last train * *Quantitative notrump bids * *Relay bids * *Splinter bid * *Serious 3NT *Defensive conventions or interventions are used to show a specific type of hand after the opponents have opened the bidding * *Takeout double * *Unassuming Cue Bid in reply to overcalls * *Lebensohl over weak two bids * *Defenses over 1 NT, including two- and multi-suited overcalls: * * * Astro, Aspro, Asptro * * * Cappelletti * * * CoCa * * * CRASH * * * DONT * * * Hamilton * * * Landy * * * Lionel * * * Meckwell * * * Multi-defense * * * Multi-Landy * * * Suction * *Two-suited overcalls over suit openings, like * * *Copenhagen convention * * *CRO * * *Ghestem * * *Leaping Michaels * * *Michaels cuebid * * *Raptor convention * * *Roman two-suiters * * *Unusual notrump *Counter-interventions present a countermeasure after opponents' conventional and natural interventions: * *Lebensohl * *Negative double * *Negative free bid * *Rubensohl * *Unusual vs. unusual *Other: * *Game trial bids * *Lightner double * *Texas transfer 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bridge convention」の詳細全文を読む スポンサード リンク
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