Systems to improve natural bidding after 1m-1M-1NT have a long history. New minor forcing (NMF) and checkback stayman had many adherents back in the day.
Right now, some form of 2-way checkback stayman is by far the most popular solution, and it is instructive to realize why. There are two main advantages of 2-way checkback stayman over its predecessors:
1. Simplicity. The system does not change according to which major you responded in, and is always very easy to handle.
2. The unbalanced hand describes. This is an important bidding principle that should be extended to as many bidding sequences as possible. It is much easier for the balanced hand to make a decision upon hearing the description of the unbalanced hand, than the opposite.
Let us examine the basic principles of the convention here. Some of the meanings I will present are not universal, since there are different versions of the convention, but I will mark them clearly with text in bold.
After the auction 1m-1M-1NT (it does not matter which minor or which major we are talking about), the meaning of the main bids are:
a. 2C: ART, forces 2D. Responder will either pass or invite with a natural, descriptive bid in the next round. All invitations based on power go through this bid.
b. 2D: ART, any GF hand that does not use another route. More about this below.
c. 2M: natural, weak. The special case of the reverse (responder bid 1H and later bid 2S) will be discussed in detail later.
d. 2NT: ART, forces 3C from partner. It is the only way to play in a club partscore, since 2C is ART, but that is not its main usefulness. If responder bids something else after bidding 2NT-3C, he is showing some other GF hands. This takes away some of the weight of the 2D GF bid.
e. 3 in a minor: distributional invitation. If the minor is a new suit, typically 4 of the major and 6 of the minor, with a hand that can envision game if it hits just the right 12-14 hand opposite.
f. Rebid of 3M: not invitational, since invitational bids based on power begin with 2C. My preferred way to play this is choice of games. 6-card suit in a semibalanced hand that can envision 3NT being the best contract. No slam interest.
Invitational sequences beginning in 2C
It is worth our while to examine all the invitational sequences available to responder.
Let us say the auction began 1 Club - 1 Spade - 1NT. After 2 Clubs - 2 Diamonds, these are the possible bids and meanings by responder:
a. Pass - Interest in playing 2 Diamonds, of course. Since this is an unbid suit, responder will often be longer in diamonds than spades (at least 4-5 is expected, 4-6 is common -- we are playing a Walsh style here).
b. 2 Hearts - invitational, natural. Responder has 4 hearts, and therefore, 5 spades, and something like 10-11 points. Opener can now pass or correct to 2 Spades or (less often) to 2NT if he does not have game ambitions. His other option is to bid a game. There is no "invite over invite".
c. 2 Spades - invitational, natural. Responder has at least 5 spades. 6 spades will be rare, but possible, since responder will be wary of risking the 3-level with a bad 6-card suit, especially since opener may very well be short in spades with a hand without reverse strength (1=4=3=5 or 1=3=4=5).
d. 2NT - invitational, natural. Responder denies 4 hearts or 5 spades.
e. 3 Clubs - invitational, natural. Denies 5 spades, since with 5 spades responder would prefer to rebid 2 Spades over 2 Diamonds, stopping at a lower level. Typically 4 spades and 5 clubs, 10-11 points (a hand with the strength to bid 2NT but which deems 3 Clubs to be the safer partscore if opener is not interested in game).
f. 3 Diamonds - invitational, natural. A non-forcing bid in an unbid suit at the 3-level requires an excellent suit, of course, usually 6 cards long, but perhaps only 5 if the quality is excellent. Denies 5 spades.
Note that 55 hands in spades and a minor will often hide the minor when inviting in spades. Since opener will often take out 2 Spades to 2NT with a singleton spade, responder will have time to bid his 5-card minor over that. If opener has 2 spades and rejects the invitation, 2 spades in the 5-2 fit will often be acceptable, even if there is a 5-4 minor fit on the side. Don't write to us if you play the wrong partscore once in a while; bridge is a game of percentages, and hiding information in the most common scenarios has lots of ways of improving your results in the long run.
g. 3 Hearts - invitational, natural, 5 cards. 55 in the majors, or better. Responder should be aware that if opener preferences back to 3 Spades, it does not show 3-card support. He will often have chosen 1NT with a 2=2=4=5 hand and prefer to play in spades now. Responder has described his hand very well and should not make a further move towards game unless he has a very special hand (e.g. 65 in the majors).
h. 3 Spades - invitational, natural, 6 good cards in the suit.
i and beyond... well, anything higher than 3 Spades is not invitational, obviously. Agreeing on a meaning for these bids puts some memory strain in your partnership. But if you feel you are up for that, here it goes:
i. 3NT - choice of games with a 5332 hand. Opener picks between 3NT and 4 Spades.
j. 4 Clubs, 4 Diamonds, 4 Hearts - Some big spade hand, that much is clear. What is the difference between this sequence (2C-2D-4x) and the immediate jump to 4x, without going through the 2C routine? With some partners, I have agreed that the longer sequence shows a void, with the direct sequence showing a singleton (denying a void). Both have slam interest, evidently. This sounds like a neat agreement, but I must confess that it never happened at the table! So, perhaps there are more useful meanings for this bid. I have been toying with the agreement that the longer sequence shows a very good suit (one that is missing, at most, one key card, and has all the other intermediates to play opposite even a singleton with at most one loser). The shorter sequence would then show an inferior suit, requiring some help in the form of lower honors (Q, J, 10), or length (e.g. AK87653). Pick your poison, or perhaps throw this glass away.
Tomorrow, we will examine responder's 2 Diamond bid and continuations. You can find the next article in this series here.