Editing Contract bridge (section)

====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.