Bidding theory is a huge subject because there are so many different auctions possible. If you're given the first few bids in the auction, you can always ask the question, what are the best meanings to give to the various possibilities for the next call? Depending on what the auction has been, it may be that natural continuations are best; or maybe you should make use of some artificial ideas such as transfers or relays or multi-way bids - or anything else you can think of. Serious partnerships could spend a huge amount of time deciding what they should do in all these different situations.
But there is one situation which is much more important than any other. That is, how will you define your opening bids? This is the aspect of bidding theory that I will be taking about in this series of posts. The opening bids are essentially what determine your "basic system", and I will be discussing what makes some systems better than others.
Let's start with one of the commonest mistakes made by amateur bidding theorists.
When you open the bidding, you can't be sure how the auction will turn out. But there are two main possibilities: either your side will have the auction to yourselves, or the opponents will come in and you will have a competitive auction. Which of these possibilities should you be more worried about?
Well, perhaps the correct answer is "it depends", but most of the time there is no doubt: competitive auctions are the important ones. The reason is simple: it's harder to reach the right contract in a competitive auction, because you have to worry about what the opponents are doing, and you usually have less space available. So, if your system works reasonably well in competitive auctions, it's can't be too bad when the opponents are silent. The converse is not true: if you come up with a set of responses which assume the opponents will be silent, it might all fall apart if they start bidding. Also, competitive auctions tend to be faster than non-competitive ones. If the opponents do not bid then a poorly defined opening bid can be corrected by a subsequent rebid, but if the auction is competitive then by the time you get to make your rebid it may already be too late.
The only time you might be more worried about constructive auctions is when the opening bid itself consumes a lot of space - particularly if it promises a good hand, as with a natural 2NT opening bid.
Admittedly, if you look at a book which describes a particular system, you will probably find that most of it is devoted to non-competitive auctions. That is the way it should be, since you can't play a system unless you know what to do in constructive auctions. Even so, it's the competitive auctions which will decide whether the system is a good one or not. I'll call this principle "Think-Competitive".
No doubt if you're reading this you will have known this principle already. But ignoring competitive auctions is a fairly easy mistake to make. I've often seen systems suggested where a 1C opening is made on a variety of possible hands, and the idea is to reveal which hand type is held with the rebid. Such systems often violate the Think-Competitive principle: if the opponents interfere at a high level, it may be too dangerous for opener to describe his hand. It is of course possible to create a workable multi-way 1C opening, but you have ensure that you can cater for all the various hand types in competition. More on this later.