Source: ABF Youth Bulletins
Assuming in a 5-card Major based system, why is it important to distinguish between 3 and 4 card support in competition? The reason is because you (and your partner) would like to get a fair idea on when to defend, and when to declare. Suppose the auction goes (you as South):
You can use 2NT as a 4 card limit+ raise, and the cuebid (3) as a 3 card limit+ raise. When you have only 3 trumps, your hand tends to be more balanced and as a result: it would be better off to defend. Similarly, when you have 4+ trumps (giving the opponents less spade cards), your hand would tend to be more unbalanced and on some occasions you wouldn’t want to be defending.
So what does this auction have to do with declaring or defending? Well, West might have the right cards to jump to 5 right away! Now, the knowledge of the possession of the 4th trump can be very crucial information to partner if he were to think about bidding 5 over 5.
Let’s say the continues as follows:
For the sake of simplicity, let’s assume 4 by partner was natural and slam try. Given that we have bid 2NT to show a 4 card limit+ raise, we are now working within the constraints that our actions over 5 would be based on hands with 4+ trumps. We could pass (forcing) to invite partner to bid on, or we could double to suggest a hand that is balanced with 4 trumps that’s not suitable for declaring.
If we were not able to distinguish 3 or 4 card support on the round before (let’s say you were playing 2NT as natural and 3 as a limit+ raise with 3+support), then you would have another factor to worry about and that is the number of trumps. So what do you do with the hands that would usually bid 2NT natural? You don’t, because they almost never come up! Think about it, to hold a natural 2NT hand you would have to have: (1) No 3+‘s, else you raise, (2) No 4+‘s, else you would make a negative double or bid 2, (3) Not 5+‘s, else you make a trap pass, (4) a hand that is exactly 10-11 HCP, else with more you can chance a double or 3NT and with less you just pass. That is a lot of conditions to satisfy thus making it a rare hand type. In the unlikely event that you do hold such a hand (i.e. 2-3-4-4), either pass and go for ‘blood’, or just bid 3NT!
Distinguishing 3 or 4 card support is even more important when it comes to major suit battles:
Now you better be prepared – how often have you seen West preempt to 4, or perhaps make a 3 preemptive jump and have East bid 4? These situations come up quite often so it is definitely a useful tool to have in your arsenal. You can also use it in defensive bidding too!