Jacoby 2NT (ie 1♠ 2NT) is an essential tool for describing good game forcing support for an opening major. Other bids
in your armoury cover support of different strengths, but without an artificial bid to cover the game forcing strengths, it is difficult to force to game, both
showing support, and describing your hand.
It is generally agreed that J2N shows 4 card support and game forcing values (whether your opening major is 4 card or 5), but beyond that there are different
treatments. For example, if you play that with a shortage you always splinter with game-forcing values, J2N will deny a shortage. The problem with
this approach is that it is then impossible to safely unravel the weaker varieties of splinter from the stronger varieties. How can opener decide to go
slamming without getting to the 5 level? For this reason my preference (and a common one) is to play that a splinter is a hand that denies the high card
values normally associated with a game force. The J2N therefore has 13+ HCP and may have a shortage.
If you play a "2 over 1" system you might bid a 5 card suit in preference to J2N, as this sets up a game forcing situation and you will support opener's major
at the next bid. This becomes useful when slamming, as opener knows there is a good source of tricks. So playing 2 over 1, J2N might deny a
decent 5 card
side suit. With Acol, this may or may not be the case, depending on your treatments.
One thing you should NOT try to do is incorporate a game invitation ("limit raise") into the 2NT reply (as some people do), because then you are severely
limiting its capabilities. The game invitation should be a different bid.
What sort of bidding follows after the J2N? This is where you need to discuss with partner, because while it is generally accepted that opener will show
a shortage if he has one, beyond that the methods are varied. Some distinguish between singletons or voids, some show side suit length, some show
This is a typical classic treatment for opener's reply:
New suit = singleton or void
3♠ = strong hand, say 17+ but no shortage
3NT = no shortage, intermediate strength 15/16
jump new suit = decent 5 card suit suit (bid this in preference to the shortage)
4♠ = no shortage, 11-14
This does have some good points, identifying strength or shortage, but there are in my view serious deficiencies:
1) it is important to convey both shortage AND strength, if partner is to have a sensible view on slam continuations
2) the minimum bid is 4♠ which then makes it impossible for a strong responder to do even
something like check for controls before ace asking
3) there is no facility for responder to show a shortage, which would let opener make a better slam judgement.
Nevertheless, this is better than nothing, and if you don't already play Jacoby 2NT then this can be easily adopted.
A suggestion for a more useful set of continuations)
The main design points have been hinted at above :
Opener should in all cases indictate his strength in the useful ranges of 12-14, 15/16, and 17+.
Opener should be able to show a shortage whatever strength range.
A minimum range opener should rebid as cheaply as possible, to allow a stronger responder to show a shortage or make investigations
without going above game.
Opener should have the option of describing additional, otherwise unknown, trump length. This can be the extra trick
needed to make a slam.
Showing strength in ranges is useful, as it makes slam discovery easier. Call these ranges "normal", "strong", and "super". Responder's strength
can similarly be categorised. Of course, while point count is a broad yardstick, you make adjustments for weaknesses like QJs in poor side suits, or
strengths like having AKs in those suits, or side suit tricks to run. However, for the run of the mill hands, a "normal" opposite a "normal" is not
usually slam material, even if there is a singleton somewhere. Normal opposite normal with a void is worth investigating, though. "Strong" is the
awkward case if there is no adequate disclosure, because when you have strong opposite strong you should be checking for slam, but neither hand can
unilaterally justify slam action. If you know partner is "strong", then it becomes easy.
A "super" does not actually need to be shown immediately, because with that hand you will take slam action even if partner does not.
Shortages (singletons or voids) in partner's hand cause you to revalue yours. A holding such as xxx is great, but KJxx is a waste of space. You
should attempt a sign-off if your hand is devalued out of the initial range; but when investigating slam you need to know whether the shortage is
void, so it is useful to have the next step as a "singleton or void" inquiry.
This leads to the opener rebids after 2NT of :
3♣ = normal 12-14, may have a singleton, will not have a void
3♦ = normal 12-14, but with a void somewhere.
3♥ = strong+ shortage in hearts
3♠ = strong+, no shortage but 6+ trumps
3NT = strong+, no shortage but only 5 trumps
4♣ = strong+ shortage in clubs
4♦ = strong+ shortage in diamonds
Once opener shows a shortage, responder is in a good position to judge the fit. As common in these situations, once you have discovered that
together you are suitable for a slam, you can turn the tables and rather than ace ask, after checking singleton or void, you give your ace response to let
partner take over. In this case, opener has a shortage and he may well have length in side suit. If responder has no particular side length, or if
he has an A/K heavy hand poor in Q/Js, it is better to let opener take control because he will be better placed to count to 13 tricks.
If opener shows the weak void hand, responder can check it out, but if opener makes the minimum 3♣ reply, a normal responder
can sign off. However, a strong responder can now show his shortage, and you still have all that space to investigate the contract level. A strong
responder with no shortage himself, however, would bid the next step to ask opener to show a singleton if he had one (he has denied a void).
In this way, opener's strength range is conveyed as well as the shortage - opener with a singleton and 12-14 bids 3♣ initially and can then show his shortage, whereas a 15+ opener will show his shortage immediately over 2NT.
Similarly a responder's splinter (eg 1♠ 4♣) is 11/12, while a 13+ can show it after 2NT.
The "strong no shortage" opener rebids are followed by cue bids, where responder can treat a shortage as a suit to cue, and responder will ask or show aces
if strong himself, but leave that decision to opener when weaker.
2NT affords room for information exchange and hand discovery. Do not waste the space. If you are playing 4♠ as
ace asking in hearts, then it makes sense to give excatly the same room for identical methods whichever major is opened, by having 1♥ 2♠ as the "Jacoby 2NT" bid.
Ray Green (fromagegb at gmail.com) revised Feb 2016