In the auction, each player calls in turn, starting from the dealer. There are 4 types of calls:
An action is a call other than pass.
Meaning of calls[]
Nearly all calls carry a meaning. The agreed meaning of a call must be made known to the opponents when requested.
A few calls do not have a meaning on their own. However, if alternatives are allowed in place of that "meaningless" call, something can be drawn by negative inference. For example, playing 2/1 GF and fourth suit artificial,
| Opener | Responder |
|---|---|
| 1♥ | 2♣ |
| 2♦ | 2♠ |
the 2♠ bid is explicitly defined as a "meaningless" bid, but the auction is still game forcing. However, the responder is known to:
- not have 3 ♥s (otherwise, he would have bid 2♥);
- not have 6 ♣s (otherwise, he would have bid 3♣);
- not have 4 ♠s (otherwise, he would have initially responded 1♠);
- not have 4 ♦s (otherwise, he would have raised 2♦ to 3♦),
therefore, responder has 3=2=3=5 shape by bidding 2♠, even 2♠ is itself meaningless.
Therefore, the only calls that are truly meaningless are calls that are forced by the system, without allowing any alternatives (including pass). For example, playing minor suit bust transfer,
| Opener | Responder |
|---|---|
| 1NT | 2♠ |
| 3♣ |
3♣ is forced by 2♠ and has completely no meaning. However, if super-accepts are allowed when playing 15-17 1NT and Jacoby transfer,
| Opener | Responder |
|---|---|
| 1NT | 2♥ |
| 2♠ |
opener is known not to have 4 ♠s and 17 points at the same time, otherwise, he would have super-accepted.
Classifying calls[]
natural vs. artificial[]
A call is called natural if its meaning is obvious, otherwise, it is artificial:
- A pass is natural if it indicates unwillingness to make any other call.
- A double or redouble is natural if it indicates willingness to increase the score of the contract.
- A bid is natural if it suggests willingness to play in that denomination.
An artificial call is a call which suggest something else other than the call itself, even with no relationship to the call itself at all:
- An artificial pass may indicate a strong hand (Strong pass system), or when an convention has been interrupted, a response (see DOPI).
- An artificial double may be used as a request to lead the double suit (Lead directing double).
- An artificial redouble may be used to rescue the partnership from a bad doubled contract (SOS redouble).
- An artificial bid may be used to initiate or respond a convention.
However, as some conventions are so widespread, they may be treated as natural in a natural bidding system, for example, as the need for penalising a low level contract is so little, a double at low level is treated as takeout, even at the natural sense.
forcing vs. non-forcing[]
Main article: Forcing
A forcing call is a call which requires partner to bid if the opponent in-between passes. A non-forcing call is a call which may be passed. There exists an intermediate type, called semi-forcing, which requires partner to bid unless he has a very specific kind of hand which should be passed, as part of the agreement.
The degree which a call urges the partner to bid are order as follows:
game forcing > forcing > semi-forcing > invitational > non-forcing > pass or correct > sign off