means a Diamond or a Club bid.
2-Over-1 Forcing ("2/1") is a convention with the following specifications:
That is the extent of the 2/1 Forcing convention. To this is often added some or all of the following additional (and separate) conventions:
Other conventions which are sometimes mentioned as being part of 2/1, such as Inverted Minors, Stayman, or Jacoby Transfers, have nothing to do with 2/1 Forcing since none of them are related to opening 1 of a major.
Some people also add 4th Suit Forcing. However, Larry Cohen says Fourth Suit Forcing is used by the responder to establish a game force. Since after a 2/1 bid, you are already in a game force, 4th Suit Forcing is redundant.
For a discussion of why 2/1 is not a "system," click here
Although 2-Over-1 Forcing is usually just called 2/1, it should not be confused with a SAYC 2/1 bid which can be made with 10-12 points. If, for example, you are a passed hand and respond 2 to partner's 1, you have bid 2/1, but you are not playing the 2/1 Convention. You are only showing 10-12 points.
In the rest of this document, a reference to 2/1 is meant to be 2/1 Forcing and not the 10-12 point 2/1.
Although sometimes called Game Forcing, 2/1 is often played as forcing only as far as the 4 level, meaning that 4 can be passed out. It also can optionally be played that if a player makes a weak response such as a simple rebid of his suit, responder can pass.
Playing 2/1 Game Forcing clarifies the bidding early for game-strength hands without having to worry about opener passing out one of your bids short of game, but it means that you cannot make a 2-level response with just an invitational hand.
For this reason, Forcing Notrump is usually played with 2-Over-1. This requires opener to bid again so that responder can clarify his hand when weak. Some play Semi-Forcing Notrump, where opener can pass with a balanced minimum hand.
If opener bids 1 and responder bids 1, 2/1 is off since the 1 bid can be made with anything from 6 points up and thus there is no game force. For this reason, Larry Cohen recommends that if responder has 4 Spades and 4+ Clubs or Diamonds and 13+ points, he should bid the minor to establish a 2/1 game force; otherwise, just bid 1.
If responder were to jump to 2 in response to 1, it would not be 2/1. It would be a jump-shift, either weak or strong, however you play it in SAYC.
Responder does not have to make a 2/1 response to 1 if some other bid is available. And before bidding a Forcing 1NT or 2/1, responder's first duty with a weak hand is to raise opener's major with 3+ of the suit. Without support and with a 4-card Spade suit, responder bids 1 over opener's 1.
With 5-11 points, no support for opener's major, and an inability to bid 1, responder should bid a Forcing 1NT.
Raising Opener's Major
With 3 trumps and
With 4+ trumps and
Forcing 1NT, continuations
Bids by responder after opener has made a second bid below 2N (usually a bid of 2)
2/1, continuation (after 1-P-2//-P)
By responder after opener's response to 2/1:
By opener after responder's 2nd bid:
The following is from Simon Stocken on BridgeWinners.com
2 over 1 after a 1 opening has 3 hands to show GF hands (excluding those with 4 card support)
After a 1 opener there are two GF bids (2 and 2).
These 2 over 1 sequences rarely occur, so on grounds of frequency it can be argued proponents of traditional 2 over 1 are 'wasting' useful bids.
A method that is becoming more popular is as follows:
2 = 8+ points, 5+ hearts
2 = 8+ points good spade raise
2 = < 8 points, 3-card raise
2 = 8+ points, good heart raise
2 = < 8 points, 3-card raise
After the 2 response there are various options (which can get complicated). The structure involves showing minimums early and transferring into an unbid major.
The advantages are considerable: