Editing Contract bridge (section)

===Bidding===
{{Main|Bidding system|Bridge convention}}

Much of the complexity in bridge arises from the difficulty of arriving at a good final contract in the auction (or deciding to let the opponents declare the contract). This is a difficult problem: the two players in a partnership must try to communicate enough information about their hands to arrive at a makeable contract, but the information they can exchange is restricted&nbsp;– information may be passed only by the calls made and later by the cards played, not by other means; in addition, the agreed-upon meaning of each call and play must be available to the opponents.

Since a partnership that has freedom to bid gradually at leisure can exchange more information, and since a partnership that can interfere with the opponents' bidding (as by raising the bidding level rapidly) can cause difficulties for their opponents, bidding systems are both informational and strategic. It is this mixture of information exchange and evaluation, deduction, and tactics that is at the heart of bidding in bridge.

A number of basic [[rule of thumb|rules of thumb]] in bridge bidding and play are summarized as [[bridge maxims]].<ref>{{Cite book |last1=Grant |first1=Audrey |url=https://books.google.com/books?id=nRbwAAAAMAAJ&q=Bridge+maxims |title=Bridge Maxims: Secrets of Better Play |last2=Rodwell |first2=Eric |date=1987 |publisher=Prentice-Hall Canada |isbn=978-0-13-081936-9 |language=en}}</ref>

====Systems and conventions====
A ''bidding system'' is a set of partnership agreements on the meanings of bids. A partnership's bidding system is usually made up of a core system, modified and complemented by specific [[convention (bridge)|conventions]] (optional customizations incorporated into the main system for handling specific bidding situations) which are pre-chosen between the partners prior to play. The line between a well-known convention and a part of a system is not always clear-cut: some bidding systems include specified conventions by default. Bidding systems can be divided into mainly natural systems such as [[Acol]] and [[Standard American]], and mainly artificial systems such as the [[Precision Club]] and [[Polish Club]].

Calls are usually considered to be either ''natural'' or ''conventional'' (artificial). A natural call carries a meaning that reflects the call; a natural bid intuitively showing hand or suit strength based on the level or suit of the bid, and a natural double expressing that the player believes that the opposing partnership will not make their contract. By contrast, a conventional (artificial) call offers and/or asks for information by means of pre-agreed coded interpretations, in which some calls convey very specific information or requests that are not part of the natural meaning of the call. Thus in response to 4NT, a 'natural' bid of 5{{Diams}} would state a preference towards a diamond suit or a desire to play in five diamonds, whereas if the partners have agreed to use the common [[Blackwood convention]], a bid of 5{{Diams}} in the same situation would say nothing about the diamond suit, but would tell the partner that the hand in question contains exactly one ace.

Conventions are valuable in bridge because of the need to pass information beyond a simple like or dislike of a particular suit, and because the limited bidding space can be used more efficiently by adopting a conventional (artificial) meaning for a given call where a natural meaning has less utility, because the information it conveys is not valuable or because the desire to convey that information arises only rarely. The conventional meaning conveys more useful (or more frequently useful) information. There are a very large number of conventions from which players can choose; many books have been written detailing bidding conventions. Well-known conventions include [[Stayman]] (to ask the opening 1NT bidder to show any four-card major suit), [[Jacoby transfer]]s (a request by (usually) the weak hand for the partner to bid a particular suit first, and therefore to become the declarer), and the Blackwood convention (to ask for information on the number of aces and kings held, used in slam bidding situations).

The term ''[[preempt]]'' refers to a high-level tactical bid by a weak hand, relying upon a very long suit rather than high cards for tricks. Preemptive bids serve a double purpose&nbsp;– they allow players to indicate they are bidding on the basis of a long suit in an otherwise weak hand, which is important information to share, and they also consume substantial bidding space which prevents a possibly strong opposing pair from exchanging information on their cards. Several systems include the use of opening bids or other early bids with weak hands including long (usually six to eight card) suits at the 2, 3 or even 4 or 5 levels as preempts.

====Basic natural systems====
As a rule, a natural suit bid indicates a holding of at least four (or more, depending on the situation and the system) cards in that suit as an opening bid, or a lesser number when supporting partner; a natural NT bid indicates a balanced hand.

Most systems use a count of [[high card point]]s as the basic evaluation of the strength of a hand, refining this by reference to shape and distribution if appropriate. In the most commonly used point count system, aces are counted as 4 points, kings as 3, queens as 2, and jacks as 1 point; therefore, the deck contains 40 points. In addition, the ''distribution'' of the cards in a hand into suits may also contribute to the strength of a hand and be counted as [[Hand evaluation|distribution points]]. A better than average hand, containing 12 or 13 points, is usually considered sufficient to ''open'' the bidding, i.e., to make the first bid in the auction. A combination of two such hands (i.e., 25 or 26 points shared between partners) is often sufficient for a partnership to bid, and generally to make, game in a [[major suit]] or notrump (more are usually needed for a [[minor suit]] game, as the level is higher).

In natural systems, a 1NT opening bid usually reflects a hand that has a relatively balanced shape (usually between two and four (or less often five) cards in each suit) and a sharply limited number of high card points, usually somewhere between 12 and 18&nbsp;– the most common ranges use a span of exactly three points (for example, 12–14, 15–17 or 16–18), but some systems use a four-point range, usually 15–18.

Opening bids of three or higher are preemptive bids, i.e., bids made with weak hands that especially favor a particular suit, opened at a high level in order to define the hand's value quickly and to frustrate the opposition. For example, a hand of {{BridgeHandInline|KQJ9872|7|42|763}} would be a candidate for an opening bid of 3{{Spades}}, designed to make it difficult for the opposing team to bid and find their [[optimum contract]] even if they have the bulk of the points. This hand is nearly valueless unless spades are trumps but it contains good enough spades that the penalty for being set should not be higher than the value of an opponent game. The high card weakness makes it likely that the opponents have enough strength to make game themselves.

Openings at the 2 level are either unusually strong (2NT, natural, and 2{{Clubs}}, artificial) or preemptive, depending on the system. Unusually strong bids communicate an especially high number of points (normally 20 or more) or a high trick-taking potential (normally 8 or more). Also 2{{Diams}} as the strongest (by HCP and by DP+HCP) has become more common, perhaps especially at websites that offer duplicate bridge. Here the 2{{Clubs}} opening is used for either hands with a good 6-card suit or longer (max one losing card) and a total of 18 HCP up to 23 total points – or "{{frac|2|1|2}}NT", like 2NT but with 22–23 HCP. Whilst the 2{{Diams}} opening bid takes care of all hands with 24 points (HCP or with distribution points included) with the only exception of "Gambling 3NT".

Opening bids at the one level are made with hands containing 12–13 points or more and which are not suitable for one of the preceding bids. Using [[Standard American]] with [[Five-card majors|5-card majors]], opening hearts or spades usually promises a 5-card suit. Partnerships who agree to play 5-card majors open a minor suit with 4-card majors and then bid their major suit at the next opportunity. This means that an opening bid of 1{{Clubs}} or 1{{Diamonds}} will sometimes be made with only 3 cards in that suit.

Doubles are sometimes given conventional meanings in otherwise mostly natural systems. A natural, or ''penalty'' double, is one used to try to gain extra points when the defenders are confident of setting (defeating) the contract. The most common example of a conventional double is the [[takeout double]] of a low-level suit bid, implying support for the unbid suits or the unbid major suits and asking partner to choose one of them.

====Basic variations====
Bidding systems depart from these basic ideas in varying degrees. [[Standard American]], for instance, is a collection of conventions designed to bolster the accuracy and power of these basic ideas, while [[Precision Club]] is a system that uses the 1{{Clubs}} opening bid for all or almost all strong hands (but sets the threshold for "strong" rather lower than most other systems&nbsp;– usually 16 high card points) and may include other artificial calls to handle other situations (but it may contain natural calls as well). Many experts today use a system called [[2/1 game forcing]] (enunciated as two over one game forcing), which amongst other features adds some complexity to the treatment of the one notrump response as used in Standard American. In the UK, [[Acol]] is the most common system; its main features are a weak one notrump opening with 12–14 high card points and several variations for 2-level openings.

There are also a variety of advanced techniques used for hand evaluation. The most basic is the [[Milton Work]] point count, (the 4-3-2-1 system detailed above) but this is sometimes modified in various ways, or either augmented or replaced by other approaches such as [[losing trick count]], [[honor point count]], [[law of total tricks]], or [[Zar Points]].

Common conventions and variations within natural systems include:
* ''[[Blackwood convention|Blackwood]]'' (either the original version or ''[[Blackwood convention#Roman Key Card Blackwood (RKCB)|Roman Key Card]]'')
* How the partnership's bidding practices will be varied if their opponents intervene or compete.
* Point count required for 1 NT opening bid ('mini' 10–12, 'weak' 12–14, 'strong' 15–17 or 16–18)
* ''[[Stayman convention|Stayman]]'' (together with Blackwood, described as "the two most famous conventions in Bridge".<ref>{{cite book |series=Bridge Lessons |title=Stayman & Transfer |at=(Deal 1) |author=Andrew Robson}}</ref>)
* What types of ''[[cue bid]]s (e.g. bidding the opponents' suit)'' the partnership will play, if any.
* Whether 1{{Clubs}} (and sometimes 1{{Diams}}) is 'natural' or 'suspect' ''(also called 'phoney' or 'short')'', signifying an opening hand lacking a notable heart or spade suit
* Whether an opening bid of 1{{Hearts}} and 1{{Spades}} requires a minimum of 4 or 5 cards in the suit (''4 or 5 card majors'')
* Whether doubling a contract at the 1, 2 and sometimes higher levels signifies a belief that the opponents' contract will fail and a desire to raise the stakes (a ''penalty double''), or an indication of strength but no biddable suit coupled with a request that partner bid something (a ''[[takeout double]]'').
* Whether doubling or overcalling over opponents' 1NT is natural or conventional. One common artificial agreement is [[Cappelletti (bridge convention)|Cappelletti]], where 2{{Clubs}} is a transfer to be passed or corrected to a major, 2{{Diamonds}} means both majors and a major shows that suit plus a minor.
* Whether opening bids at the two level are 'strong' (20+ points) or '[[Weak two bid|weak]]' (i.e., pre-emptive with a 6 card suit). (Note: an [[Strong two clubs|opening bid]] of 2{{Clubs}} is usually played in otherwise natural systems as conventional, signifying any exceptionally strong hand)
* Whether the partnership will play ''[[Jacoby transfer]]s'' (bids of 2{{Diamonds}} and 2{{Hearts}} over 1NT or 3{{Diamonds}} and 3{{Hearts}} over 2NT respectively require the 1NT or 2NT bidder to rebid 2{{Hearts}} and 2{{Spades}} or 3{{Hearts}} and 3{{Spades}}), ''minor suit transfers'' (bids of 2{{Spades}} and either 2NT or 3{{Clubs}} over 1NT respectively require the 1NT bidder to bid 3{{Clubs}} and 3{{Diamonds}}) and ''Texas transfers'' (bids of 4{{Diamonds}} and 4{{Hearts}} respectively require the 1NT, or 2NT bidder to rebid 4{{Hearts}} and 4{{Spades}})
* Which (if any) bids are ''[[forcing bid|forcing]]'' and require a response.

Within play, it is also commonly agreed what systems of opening leads, signals and discards will be played:
* Conventions for the [[opening lead]] govern how the first card to be played will be chosen and what it will mean,
* Count signals cover the situation when a defender is following suit (usually to a suit that the declarer has led). In such circumstances the order in which a defender plays his spot cards will indicate whether an even or odd number of cards was originally held in that suit. This can help the other defender count out the entire original distribution of the cards in that suit. It is sometimes critical to know this when defending.
* [[Discard (bridge)|Discards]] cover the situation when a defender cannot follow suit and therefore has free choice what card to play or throw away. In such circumstances the thrown-away card can be used to indicate some aspect of the hand, or a desire for a specific suit to be played.
* [[Signal (bridge)|Signals]] indicate how cards played within a suit are chosen&nbsp;– for example, playing a noticeably high card when this is unexpected can signal encouragement to continue playing the suit, and a low card can signal discouragement and a desire for partner to choose some other suit. (Some partnerships use "reverse" signals, meaning that a noticeably high card ''discourages'' that suit and a noticeably low card ''encourages'' that suit, thus not "wasting" a potentially useful intermediate card in the suit of interest.)
* [[Glossary of contract bridge terms#SPS|Suit preference signals]] cover the situation where a defender is returning a suit which will be ruffed by his partner. If he plays a high card he is showing an entry in the higher side suit and vice versa. There are some other situations where this tool may be used.
* [[Glossary of contract bridge terms#Surrogate Signals|Surrogate signals]] cover the situation when it is critical to show length in a side suit and it will be too late if defenders wait until that suit is played. Then, the play in the first declarer played suit is a count signal regarding the critical suit and not the trump suit itself. In fact, any signal made about a suit in another suit might be called as such.

====Advanced techniques====
Every call (including "pass", also sometimes called "no bid") serves two purposes. It confirms or passes some information to a partner, and, by implication, denies any other kind of hand which would have tended to support an alternative call. For example, a bid of 2NT immediately after partner's 1NT not only shows a balanced hand of a certain point range, but also almost always denies possession of a five-card major suit (otherwise the player would have bid it) or even a four card major suit (in that case, the player should use the [[Stayman convention]]).

Likewise, in some partnerships the bid of 2{{Hearts}} in the sequence 1NT–2{{Clubs}}–2{{Diams}}–2{{Hearts}} between partners (opponents passing throughout) explicitly shows five hearts but also confirms four cards in spades: the bidder must hold at least five hearts to make it worth looking for a heart fit after 2{{Diams}} denied a four card major, and with at least five hearts, a Stayman bid must have been justified by having exactly four spades, the other major (since Stayman (as used by this partnership) is not useful with anything except a four card major suit).<ref>{{cite book |author=Andrew Robson |series=Bridge Lessons |title=Stayman & Transfer |at=(Deal 14)}}</ref> Thus an astute partner can read much more than the surface meaning into the bidding. Alternatively, many partnerships play this same bidding sequence as "Crawling Stayman" by which the responder shows a weak hand (less than eight high card points) with shortness in diamonds but at least four hearts and four spades; the opening bidder may correct to spades if that appears to be the better contract.

The situations detailed here are extremely simple examples; many instances of advanced bidding involve specific agreements related to very specific situations and subtle inferences regarding entire sequences of calls.