We have talked about rebids on each occasion where they have come up along the way, but there is much more that needs to be said about them. The first level of bidding is usually quite straight forward and there are rules which make it quite simple to decide whether to bid, and what to bid. But when you come to rebids, you get into the realm where you need to be able to decide whether this hand is going to lead to a game contract for you and your partner, or whether it is best to let the bidding die at a low level.
As an opening bidder, you might have a weakish opening hand (12-15 points) and if you got weak reply from your partner, then you should not progress any farther. For instance if you bid 1 Club with 13 points, and your partner said 1 No Trump, meaning 6-10 points, that he doesn't particularly like your clubs, and that he has no better suit to offer at the one level, then your choice is to leave him in the 1 No Trump, or if you have 5 Clubs, to repeat them. You can bid a 4 card suit to bid the first time the suit is mentioned, but if you are going to rebid, you need to have 5.
Sometimes you have 2 more or less equal suits and the rule is that if these are 5 cards suits, you bid the higher ranking first and rebid with the lower ranking. So if you had 5 Hearts and 5 Diamonds, you would open with 1 Heart, and when you partner replied (perhaps with 1 Spade) you can rebid now with your lower ranking suit, which would be 2 Diamonds. From your bidding, your partner would know that you had 5 Hearts and might have 5 or 4 Diamonds. He would then be expected to choose between those two suits whichever he preferred for the contract, unless his Spades were so strong that his only option would be to repeat them.
However, if you have 2 more or less equal four card suits, you would bid the lower ranking first. So if you had 4 Clubs and 4 Hearts, you would open with 1 Club, and if your partner said 1 Diamond, you could rebid with 1 Heart. However, if your partner bid 1 Spade or 1 No Trump, it would be more difficult for you to rebid with the Hearts on the 2 level, as that would promise quite a good hand.
Sometimes there isn't a clear and easy rebid to make. That is why the weak No Trump is such a useful bid. When you have bid that, you don't have to bid again - you have already told all there is to tell about your hand and it is up to your partner to decide where to go from there.
If you have a medium-strong opening hand (15-18 points) then you can afford to give a rebid on a higher level, rather than let the bidding die at an early stage. Here you are clearly in a situation where you might well have a game on, but need to know a bit more before you make the final decision.
With a very strong hand (19 + points) you will have almost decided before you started bidding that you will carry on to the game level, with only the slightest encouragement from your partner.
But since the weak opening hands are the most difficult to know what to do with, let us have a set hand to work through and see if it will become clearer.
Let's say this is your opening hand. When you have 3 biddable suits, there is a convention for which one to choose. If you have a red singleton, you start with the suit below your singleton. If you have a black singleton, you start with the suit in the middle.
32. What would you open on this hand?
a. 1 Diamond
b. 1 Heart
c. 1 Spade