This post gets me back to a segment of my audience that I may have ignored recently, the novice/aspiring intermediate. Jacoby 2NT is a direct 2NT conventional response to a major suit opened by your partner. It shows 4 card trump support and game going values. If you play Bergen raises, then you already have a bid for the hand that has 10-12 hcps and 4 card support, so you could reserve Jacoby 2NT for hands with 13+hcps. If you do not play Bergen raises, then I think it is all right to drop the requirement down to the 12 hcp range. In final result, shape makes a great deal of difference and in valuing the hands, responder should consider that he is a supporting hand, not an opening hand.
In an earlier post I discussed splinter bids at length (see January 07 archives). There is some overlap between Jacoby 2NT and splinter bids. My rule is that I do not use Jacoby 2NT if I have the requirements for Jacoby 2NT, but also contains a single or void. I would make a splinter bid instead.If you don't usae splinters, just ignore this concept.
Here are the standard responses to a Jacoby 2NT bid:
1. If opener has a single or void, he bids that suit. That is the first priority no matter what the size of the hand.
2. The next priority is to show the size of the hand if there is no single or void.
(a) With a minimum (14 hcps or less) bid 4 of the major. This is the fast arrival concept and warns partner that you do not have any significant extras.
(b) With 15-17 hcps and no single or void, bid 3NT.
(c) With 18+ hcps and no single or void, bid 3 of the major.
Note you jump to game when you have a minimum hand and slow bid it when you have extra values.
One minor point. If you have a good 5+ card suit (AK10xx or AQJxxx), you ignore all the rest of the instructions and make a jump bid in that suit. So the sequence 1h/2NT/4C shows a good 5 card club suit. Literally, a source of tricks on which responder may be able to pitch losers. Some prefer that the jump bid show a void to distinguish it from a singleton, but I like it the way I have explained it. If I have a void and think it is something that partner needs to know, I will bid the suit at the 3 level and bid it again a the 4 level if I have the chance to do so.These are refinements that rarely arise and can slow you down, so don't get bogged down here.
You can see that opener is describing his hand, so responder must be the Captain of ship in these sequences. If Responder has any interest in pursuing slam, he should not bid 4 of the major, as opener will correctly pass. One way to invite slam is to go directly to Blackwood or whatever you use to ask for Key cards. Unfortunately, there are some hands where you can only pursue slam if partner holds a specific Ace. An alternative to Blackwood is to bid first round controls up the line. Look at these hands:
(Opener) AK10xxx, xx, AQxxx, Kx (16 hcps)
(Responder) Jxxx, AKxx, Kxx, Qx (13 hcps)
The bidding: 1s/2NT/4S (no single or void and 12-14 hcps). Responder has a great hand with 2 doubletons and lots of Aces and Kings. He does need to know about the Ace of hearts since if opener does not have it, he would have 2 losers off the top. The best way to invite with this hand is not Blackwood, but rather by showing the diamond Ace by bidding 5 diamonds and asking opener to further describe his hand. We have already established that spades is our fit, so this can only be a first round control showing bid, not a new suit at this level. Your plan is that if partner bids 5 hearts showing the Ace of hearts, you are going to play 6 spades and if partner doesn't have the Ace of hearts, he will bid 5 spades to play. On the above hands we get to a cold slam on 29 hcps. There is no other way to get there other than to guess.
Note that if partner has the Ace of Clubs and not the Ace of hearts, he has to ignore it and bid 5 spades. You cannot show a control beyond the 5 level game. If you are going to use Jacoby 2NT, it is a good thing to discuss it with partner in advance, since many players do not understand it beyond the 2NT bid, and you are better off without it if you do not know the basic concepts and continuations.