Jacoby tranfers are bids that use one artificial bid to invite the partner to “transfer” the bid to another suit. Transfer bids only occur after a 1 No-Trump opening bid. The strategy behind transfer bids is to try and find a fit in a major suit (Spades or Hearts) but in such a way that the better of the two hands (the one that opened with 1 NT) gets to be the Declarer and can keep his/her hand hidden from the opponents. Therefore, this system of transfer bidding does not give the opponents any clue as to where to attack on defense when they have the lead.
If you use all natural bids, here’s how an auction often would go:
|1 NT||Pass||2 ♠||Pass|
|3 ♠||Pass||4 ♠||Pass|
This is a typical hand in which South has 15-17 points and North has 9-10 point support with a five-card Spade suit (and South has 3 Spades to support, perhaps with an honor).
Now North has to play the hand because he/she is the first one to have bid Spades. This leaves the good hand with most of the points exposed as the dummy. Now the opponents can take potshots at the dummy and its weaknesses (every hand has some), depending on who’s on lead. Remember, dummy on the right, lead the weakest thing in sight; dummy on the left, lead through heft (meaning if there’s a suit there with a hole in it, like Ace-Queen, the opponents will lead through that strength trying to find the King that’s sitting behind that power. Therefore, the opponents now have all the clues as to the best line of defense to defeat the contract.
To prevent that, you play “Jacoby transfers,” meaning that you make sure the roles between Declarer and dummy and transferred. The way you do that is for the responder to the 1 NT opener to make a bid that is one under the one you really want to bid. It only applies when you have a five-card suit. (If you have a 4-card major, you bid 2 Clubs under the separate Stayman convention.) So if you have five Hearts as a responder to a 1 No-Trump opener, you bid 2 Diamonds (the bid you really wanted to make was 2 Hearts, so you bid the next lower bid). And if you bid 2 Hearts, it means you have five Spades. (Some people play transfers to majors and minors; so 2 Spades would mean “I have five Clubs” and a 3 Clubs bid — remember, 2 Clubs is not available because it would be a Stayman response — means “I have five Diamonds.”)
If the 1 NT opener likes the suit that was indicated by the artificial “transfer” bid (for example, Hearts, in the case of the 2 Diamonds bid), then the 1 NT opener will now say 2 Hearts, “accepting” the transfer and ensuring that if the contract is played in Hearts, the strong hand with the 1 NT opening is the Declarer and his/her hand remains hidden and does not give the opponents any clues as to what to lead.
If the transfer bid is “accepted” (in other words, the 1 NT opening hand bids the suit that the responder invited him/her to bid with the artificial “transfer” bid) with the 2 Hearts bid, it is now up to the responder to determine whether the contract will be played in 2 Hearts, 3 Hearts or 4 Hearts (or perhaps even higher, in Slam). Here the responder becomes the captain of the ship under the captaincy theory of play. The responder knows that the 1 NT opening hand has 15-17 points with a pretty even distribution. Therefore, if the responder has fewer than 8 points, it is best to pass the 2 Hearts — you probably don’t have enough values for Game.
If you have 8-9 points, you may say 3 Hearts as an “invitational” bid to invite your partner to go to Game is he/she is at the upper edge of the 15-17 NT range. If you have 10-11 points, you should go straight to Game in 4 Hearts. If you have 12 points or more, you may start thinking about Slam by asking for Aces because if partner is at the upper point range, you now have 29 points between you, the minimum for starting to think about Slam.
Most 1 NT opening bidders will accept the transfer and bid the suit in which the responder has a five-card suit. After all, they opened with 1 No-Trump and have no suit shorter than a doubleton, so they have at least two cards in the suit, guaranteeing a bare seven-card majority. However, the responder may then still bid 2 No-Trump to give the original opener the option of playing the contract in No-Trump is his doubleton in the suit is really weak. The 1 NT opening hand does not have to accept the transfer. Suppose the responder has said 2 Diamonds indicating a five-card Heart suit, but the 1 NT opening hand has only 2 low Hearts, the opening bidder may not accept the transfer to Hearts. If the opener has a five-card Spade suit, he/she may say 2 Spades, hoping partner has 3 of them and can support them. If the 1 NT opening hand has nothing useful in either major suit, he/she may bid a 5-card minor suit or 2 NT and the auction will likely go toward a contract in No-Trump or a minor suit (likely not Game since 5 may be too high).
Jacoby transfers are also still on after a stronger 2 No-Trump opening indicating 20-21 points. Instead of 2 Diamonds meaning “I have a five-card Heart suit) it just becomes 3 Diamonds, meaning the same thing.
It may get a little complicated after interference and the details will depend on partnership agreements. The first opponent to bid after the 1 NT opening bid may throw in a 2 Diamonds bid. If that’s the bid that the 1 NT responder wanted to make (indicating a five-card Heart suit), the responder may just “double,” telling partner that “he/she took my bid.” If the interference has bypassed the bid that the responder wanted to make (for example, the opponents’ interference bid was 2 Spades and the responder had wanted to day 2 Diamonds), then the responder may just go to the 3 level and bid 3 Diamonds. The partner will still interpret it as meaning “I have 5 Hearts.” With most of my partners, I have agreed that transfers to the minor suits are off after interference, because they may get you too high too fast.