The Case for the Weak NT: Playing the wrong partscore

After a 1NT opening there is always a risk of a missing a 4-4 major fit on a partscore hand. The weak notrump occurs with greater frequency which makes this more likely and also the extra strength of the strong notrump means that 1NT will still often make when a better spot is available. To actually lose IMPs this way, though, several things have to happen:

1. 1NT has to go down while 2 of a major is making
2. The opponents must remain silent over 1NT. If they bid, you can make a takeout double and still find your 4-4 fit.
3. The opponents must not be able to successfully outbid you. It is risky to enter the auction over 1NT, while balancing when opponents bid and raise at the two level is relatively safe. So you might never be able to play 2 of a major anyway.

About 13% of hands qualify for a weak notrump opening. On about 10% of these, responder will pass when you have a 4-4 major fit. Moderately aggressive opponents will only let you play in 1NT on about 20% of such hands. Overall, this is about one in every 770 hands, not including those where they can successfully bid over your two of a major but would pass 1NT, or where the 1NT contract does as well as, or better than, two of the major.

You can also alleviate the problem by responder using Stayman on weaker hands with 4-4 in the majors. As long as partner doesn't open 1NT with 2254 or 2263 shapes you'll play a 4-3 at worst which may still be better than 1NT. It's better to have two decent suits for this as three trumps opposite four small ones doesn't usually play well. You also need to agree that after 1NT-2C-2D-2H opener must correct to 2S holding three spades and two hearts.

There is also a corresponding situation where a 1NT opening makes it easier to locate an eight card major fit. This is where opener is balanced and responder has a five card major. After a 1NT opener, responder will transfer and pass. After a 1C/D opening and responder bids his major, opener may raise with three cards or bid 1NT. If he bids 1NT responder will pass and the eight card fit will be lost. If he raises, you'll play a 4-3 fit some of the time and the range of opener's raise is uncomfortably stretched if it may include a weak balanced hand with three card support. Playing a 5-2 when responder transfers and passes is less likely to be wrong than missing a 5-3. The extra frequency of the weak notrump is therefore a benefit on these hands. Furthermore, when 1NT is not opened, a three card raise on a balanced hand is not a stretch as opener will have 15+ HCP.

Finally, after opening one of a minor with 12-14 balanced it is not clear what is supposed to happen with a 4-4 fit when responder does not introduce the suit immediately, e.g. opener has four spades and the auction starts 1C-1H. If opener bypasses 1S and rebids 1NT, you lose spades when responder is too weak to act so are in the same position as a weak notrump opener except your two extra bids have helped the defence. If opener bids 1S instead of 1NT you risk playing 1NT from the wrong side or not at all when that is the best contract.

To summarise, opening 1NT may risk missing a 4-4 major fit on a partscore hand and the weak notrump does make this more likely. However this is much less frequent and less serious than is commonly believed, and in any case such hands will not usually end quietly in two of a major after a minor suit opening. There are other situations where a 1NT opening makes it easier to correctly find a major suit part score.