Remember there are 40 Honour points in the pack.
Lets assume that you need 25 (occasionally 24) to make 9 tricks most players will stop short
of the three level with 23 or less.
This doesn’t mean that you should never bid on; just be aware that you are less likely
to make your contract, but then so are the opposition.
But, as we know, points aren’t everything in Bridge; distribution is a major factor.
The Law of Total tricks is a very complicated business. One of the books on it is actually called
“To bid or not to bid”
One of the principles described is The Law of Total Trumps.
In its simplest form it can
used to make that all important decision on how high to compete in a part score battle .
It says: the number of tricks you can make is approximately equal to the total number of
trumps held between both hands,
with the proviso that you should also hold in the area of required high card points, say in this case
about 16-23.
Here is a simple example:
You open 1 ♠ with 12 points
and 5 Spades. Partner bids 2 ♠ generally guaranteeing 4.
You have about 18-21 points between you but 9 or more Spades. Obviously with no opposition
bidding you would stop in 2 ♠
But suppose the bidding goes 1 ♠-2♥-2 ♠-3♥ back to you. The total tricks are: Your side at least 9 , the opposition at least 8 .
So theoretically you can make 3 ♠ but they can only make 2♥ but they might hold 9 trumps and make their contract.
But, of course, how many tricks you actually make depends on many more factors;
Does a finesse work? You hold Kxx in an outside suit- Who holds the Ace?.
If they are wrong for you then they are right for the opposition.
Then your 9 becomes 8 and their 8 becomes 9 so you bid to 3 ♠
In this example you wouldn’t have opened 1 ♠ with only 4 Spades
and 12 points but with lower ranking suits if you Pass Partner should also pass with 4 but bid on with 5.
It doesn’t always work (nothing does in Bridge) but it does more often than not.
Finally, I have quoted from Tony Forrester's excellent “Secrets of Success ”
elsewhere on this web site.
Here what he has to say on this subject.
It is rarely good bridge to defend at the two level with a nine card fit
But he goes on to say that your decision to compete should be based on the length that
you hold in the opposition's suit
He summarizes with be careful if you hold three cards in the opponents suit,
be willing to gamble with two and consider it almost automatic with one
The above is only a fairly simple analysis, much more has been written on the subject,but I hope it covers the general principle.