The Case for the Weak NT: Summary

So far we have seen:

Both the weak and strong notrump carry negative inferences that are useful after opening one of a suit. However, because the weak notrump includes all of the weakest playing strength opening hands, it has the effect of increasing the lower limit of your other one level openings. This is a big plus.

The strong notrump leads to awkward rebid problems on unbalanced hands in the 15-17 range. This is less of a problem with the weak notrump as the suit opened can be rebid with a minimum opening and 1NT is available with a better hand.

Missing a 4-4 major fit is a possible disadvantage for the weak notrump, but this happens much less often than is commonly believed and need not always lead to a bad result even when it does occur.

The side that opens 1NT is much better placed in the subsequent auction. A weak notrump means this advantage is enjoyed more often. A weak notrump opening also means the opponents need to consider whether they have a game or can extract a penalty, in addition to just locating their best partscore. All of this in the very limited space available to them when you have started with 1NT.

Finally, a computer analysis of the likelihood of being doubled for a penalty after opening 1NT shows you can expect a 10 IMP loss once every 800 hands, under assumptions very favourable to the opponents. Under more realistic assumptions, the loss is probably miniscule or non-existent.

I would like to conclude by pointing out that the weak notrump works just as well with a five card major system and 2/1 game force as it does with Acol or similar systems. Do try it!