Five-card majors is a contract bridge bidding treatment common to many modern bidding systems. Its basic tenet is that an opening bid of one-of-a-major in first and second position guarantees at least five cards in that major. This method has become standard in North American tournament play, but European methods vary.
Typically when a bridge player makes a natural bid in a major suit (hearts or spades), he is promising at least four cards in that suit and asking partner if it will be an advantageous trump suit for the partnership. Because of the power of naming a trump suit with an eight-card fit, the responder with four or more cards of that suit will support his partners bid as if to say "we have found our eight-card fit."
If the opening bid promises five cards in the suit rather than just four, and responder holds three-card support, the 5-3 fit will be found immediately, rather than after opener's rebid. A 5-4 fit will also be found immediately, although a 4-4 fit will be found only after partner's first response. Since finding major suit fits is a high priority, making opening bids of 1♥ and 1♠ promise five cards rather than four is attractive.
Five-card major systems have the following advantages compared to four-card majors:
However, they have the following disadvantages compared to four-card majors (particularly where, in hands with a four-card major and a four-card minor, the major is opened):
With 13 cards in each suit, an eight-card fit implies that only five trump cards can be held by the opponents. They will most likely be distributed 3-2 or 2-3 among the opponents, so playing trump for three rounds will probably draw all trump cards from the opponents and leave two additional trump to be used separately for offensive purposes. However if the trump cards break 4-1 or 1-4, then drawing trump will result in no trumps left for offensive purposes.
The value of five-card majors can be understood then on two levels:
But five-card majors have several drawbacks:
Both partners must agree to follow the five-card major bidding treatment on their opening bid. Opener must have at least five cards in hearts or spades to start the bidding with that suit. Responder is expected to show support with three-card support, indicating an eight-card fit. With only four cards in a major suit, the opening bidder is expected to open one of a minor suit (which may show less than four cards in that suit) or 1NT if in the agreed points range. After the opening bid, the five-card limitation is no longer in effect and any other bid typically promises only four cards as before.
Bridge partnerships who use five-card majors need some kind of short club opening bid. The most common practice is for 1♣ to promise at least a three-card club suit, indicating that opener has:
In this case, a 1♦ bid may also be on three cards, to cope with a 4-4-3-2 shape. This method is used in Standard American bidding. The alternative is for 1♦ to promise at least four cards, in which case the 1♣ opening may have to be made on a two-card suit.
There is strong pressure upon responder to bid a four-card major even after an intervening bid, or to show it indirectly by a negative double. In some methods, 1♣ - (1NT) - 2♥ as first response may promise only four hearts. Opening bidder will not raise the 2♥ bid with only three hearts.
Most bidding systems use five-card majors in conjunction with a strong no-trump. However, it is also possible to play it with a weak no-trump, as practiced by some club and tournament players in the United Kingdom.