The Case for the Weak NT: Inferences when 1NT is not opened

Balanced hands in the 12-14 range have the least playing strength of all opening hands. Therefore, the weak notrump effectively increases the minimum strength of opening bids of one club and one diamond so these have a narrower range. Conversely, the strong notrump removes intermediate range hands from the one of a minor openings. Consider the following hand:

♠	Qxx
♥	AKxx
♦	xx
♣	AKxx

LHO makes a preemptive jump to 3S over your opening bid. Partner passes. There is no problem if you opened a strong notrump as you've shown extra strength already so have no reason to bid more. It's more difficult if you opened 1C playing a weak notrump. Suppose you pass 3S. Consider three possible hands for partner:

♠	x	♠	Jx	♠	xx
♥	Qxx	♥	Qxx	♥	Qxxx
♦	Axxxx	♦	AJxxx	♦	Axxx
♣	Qxxx	♣	Qxx	♣	Qxx

The first hand gives some play for 4H or 5C though I think partner might double, rather than pass. The hand with shortness needs to take the lead in these situations. It would be nice to have a fourth heart but a 4-3 fit could be ok. Even playing a strong notrump, there are plenty of hands where you want to be in the auction but it will be hard for opener to act after a pass.

The second hand is probably close to a maximum pass. You might make 3NT but it needs some luck. Likewise the third hand is marginal for 4H and partner would double if stronger.

Examples like this suggest to me that it's acceptable to pass an average strong notrump in this situation. Also bear in mind that partner can make a negative double a bit more freely playing a weak notrump as he knows you won't have a weak balanced hand. And none of the above would be straightforward if the opening bid was a 15-17 1NT instead of 1C.

Playing a weak notrump, the inferences after a 1C/D opening occur in situations such as the following:

♠	AQJxx		♠	K10xx		♠	K10xx
♥	xxx	opposite	♥	Axx	or	♥	Ax
♦	xx		♦	AQxx		♦	AQxxx
♣	Qxx		♣	xx		♣	xx

In each case, the bidding starts 1D-1S-2S. Opposite the first hand, you cannot make game and are in danger at the three level. With the second, game is close to 50% and worth bidding at IMPs. Removing hands such as the first one by opening them with 1NT means opener's playing strength falls with a narrower range and decisions about whether to bid game are therefore more accurate. What tends to happen playing a strong notrump is that opener will stretch to bid 3S on hands not much stronger than the second, which may well lead to a hopeless contract opposite a minimum responder.

The exclusion of strong notrump hands from an opening bid of one of a minor does not carry any such useful inference as opener may still have an unbalanced hand of equivalent playing strength.