A Preference or a Raise?
There are subtle elements to bidding that may not be easy to detect when you are just starting out.
Here are two auctions.
Both auctions conclude with South bidding 3 ♠. Can you tell the difference? In the first, South had a hand worth a jump (limit) raise to 3 ♠ but he did not have the requisite four trumps in the modern style. The only way to show that hand is to bid 1NT as a one-round force, then make the jump bid, describing a hand with three-card spade support and limit-raise (game invitational) values.
As for the second auction, South's bid of 3 ♠ says only that he had enough to keep the bidding open and that he likes spades better than hearts. South is showing a relatively weak hand with two-card spade support at best. With modest values and at least three spades, South would have made a simple raise in spades rather than bidding 1NT.
When your partner opens the bidding and you have a hand just barely good enough to keep the bidding open, make your bid as descriptive as possible. It may be your only chance to bid. Always keep in mind the maxim: Support with support.
In the case of the second auction, 3 ♠ is not a raise, it is a preference. South makes no promises about his spade holding. All he is saying is, “Partner, I understand that you have a very strong hand with spades and hearts. Based on that information, 3 ♠ is where I want to play this contract. If you bid on to game, you do so on your own.”
There will be occasions when your partner enters the auction at a high level, forcing you to bid. The following occurs more often than you might think:
South's 4NT describes a two-suited hand with the minors. The 5 ♣ bid does not say anything about North's hand except that she prefers clubs to diamonds. North could have:
5 ♣ is in no way a forward-going bid. North was forced to choose between the minors, and she did so. South should not infer anything from the bidding except that North likes clubs betters than diamonds.
It's a completely different matter when the bidding is done freely, for example:
In this case, North is doing more than taking a preference when South shows the minors with his bid of 2NT. North believes she has the values to compete in addition to a good trump fit. If there is anything the least bit exceptional about the South hand — perhaps five diamonds, six clubs, and a void — it will behoove that player to bid on.