At my local bridge club there are three pairs playing a strong club system and two of those employ a 12-15 no-trump opening. Should you treat that as a “strong no-trump” or as a “weak no-trump”?
What is the issue?
An opening 1 NT in standard American bidding shows a balanced hand with 15-17 high card points (hcp). When the opponents open this standard “strong no-trump” most of us have partnership agreements in place. But what if the opponents alert their opening 1 NT bid as 10-12 high card points? Are you ready for that “weak no-trump”?
Many no-trump defense systems do not use a double for penalty, e.g. DONT, Brozel, SCUM, Suction, etc. The idea is that successfully punishing a 15-17 no-trump opening is a rare event. So, let’s use the double for something more productive.
But when the opponents open a 10-12 no-trump—you will often want to double for penalty. This might even be your most common response.
Having a separate defense system for weak no-trump openings raises the question: do I treat their 1NT as weak or strong?
For many of the popular no-trump ranges there is general agreement—
10-12 weak
10-13 weak
11-14 weak
12-14 weak
14-16 strong
14-17 strong
15-17 strong
The most controversial range is 12-15. For this weak vs strong decision, a common heuristic is “If their range contains 15 then treat it as strong”. By that agreement 12-15 will be classified as strong. Let’s look at that choice.
We start by agreeing that the 12-14 range is weak and the 15-17 range is strong. Now, is an announced 12-15 no-trump opening more likely to be in the 12-14 bucket or the 15-17 one?
The exact probabilities for 12-15 point hands are
12 – 8.03%
13 – 6.91%
14 – 5.69%
15 – 4.42%
12-15 – 25.06%
For 15 hcp we have P(15) / P(12-15) = 4.42 / 25.06 = 17.65%.
This means that only 17.65% of the time a 12-15 no-trump will be 15 (“strong”) and the remainder (82.35%) of the time it will be in the 12-14 point range (“weak”). I conclude that the correct heuristic should be “If their range contains 12, treat their no-trump as weak”.
As someone who regularly plays a 12-15 no-trump I am relieved to hear the opponents agree to treat my 12 point openings as strong. It makes my no-trump opening preemptive with limited risk.
References–
Strong club systems with 12-15 no-trump:
Sensible Big Club
UnBalanced Club
Probability distribution of high card points:
Chart
Table
