The general approach when you are interested in a slam is to cue bid first- and second-round controls equally and then use Roman Key-Card Blackwood (RKCB) to check that you have sufficient key cards to make a slam.
A cue bid can be a first-round control, namely an ace or void, or a second-round control, namely a king or singleton. We do not cue bid shortage in partner’s main suit because otherwise they will not know if it is a high-card or shortage: imagine that they hold ♠KQ1095; if they hold the ace of spades, then it is a great holding but if it is a void or singleton it is not.
If we miss a suit, then we do not hold a control in that suit. If partner continues to cue bid, or bids RKCB, then partner guarantees a control in the missed suit.
A second cue bid in a suit shows first and second round in the suit - singleton ace or both ace and king in the suit. Perhaps mention that if you show shortage (by means of a splinter) and then you cuebid the same suit again, that should be a void. (Rare, but helpful to know.)
Cue bidding is particularly valuable when you need controls in a specific suit to bid the slam or you have a void and RKCB will not help you discover if slam is a good proposition.
A 4NT bid is normally Roman Key-Card Blackwood (RKCB) asking for the number of key cards, which are the four aces and king of the agreed trump suit. It is also extended to show the queen of the agreed trump suit.
The following are examples of 4NT RKCB:
1♠ 2♥ 1♠ 3♠
2♠ 3♠ 4NT
4♣ 4NT
If a key suit exists, the king of that suit counts is counted as an ace so there are 5 key cards. As we play 1430 RKCB, the responses are as follows:
Step 1 5♣ 1 or 4 key cards
Step 2 5♦ 0 or 3 key cards
Step 3 5♥ 2 or 5 key cards without key suit queen
Step 4 5♠ 2 or 5 key cards with key suit queen
Step 5 5NT 2 or 4 key cards with a useful void
Step 6 6X 1 or 3 key cards and a void in suit bid, if below agreed suit
Step 7 6X 1 or 3 key cards and a void in higher ranking suit, if agreed suit
Note that some partnerships swap the 5♣ and 5♦ responses (so they play 3041 RKCB). Obviously five key cards are rare, since the weaker hand would not be invoking RKCB without holding any key cards.
Example:
AK1063 Q
QJ3 A109876
Axx KJ10
Ax K32
1♠ 2♥ (2/1, FG)
3♥ 4♣ Despite holding a minimum 2/1 response, your controls
are good, you have a sixth heart, and partner’s 3♥
bid is unlimited. You did not cue bid shortage in
partner’s suit.
4♦ I have spade control (since you bypassed it) and a
diamond control.
4♥ Although I also have a diamond control, I am not strong
enough to go above the game level. I have shown some
slam suitability by cue bidding once.
4NT I could have bid this last time, but I wanted to see if we
were thinking of small slam or potentially a grand slam.
As you are not strong enough to go on yourself, small
slam is the limit.
5♣ One key card.
6♥ We should have sufficient for small slam with just one
trump loser possible.
The continuation structure is the same after all key-card auctions. The steps are:
After the queen ask, responder returns to trump suit to deny the queen, otherwise suit bids show the king of the bid suit or two kings excluding the bid suit, eg (spades agreed as trumps)
4NT P 5♣ P Showing 1 or 4 key cards
5♦ P ? Asking for the spade queen?
5♥ spade queen, shows ♥K or both minor kings
5♠ no spade queen
5NT spade queen, three kings (!)
6♣ spade queen, ♣K or both red kings
6♦ spade queen, ♦K or both rounded kings
After all responses new suit (except next suit up after 5♣/♦) asks for that king, responder replies as above returning to trump suit to deny otherwise bidding lowest king not held. Blackwooder continues to ask as much as he want responder shows.
Example, hearts agreed trumps
4NT P 5♥ P 2 key cards without the trump queen
5♠ P ? Asks for kings
5NT spade king or both minor kings
6♣ club king, or spade and diamond kings
6♦ diamond king, or both black kings
6♥ no kings
Example, spades agreed trumps
4NT P 5♠ P 2 key cards and the trump queen
5NT P ? Ask for kings
6♣ club king OR 2 other non-club kings
6♦ diamond king OR heart and club kings
6♥ heart king or 2 other non-heart kings
6♠ no kings
Example, hearts agreed trumps
4NT P 5♦ P 0 or 3 key cards
? 5♥ to play
5♠ asks for queen of trumps
5NT asks for kings
6♣ do you have club king?
6♦ do you have diamond king?
6♥ to play
Example, hearts agreed trumps
4NT P 5♦ P 0 or 3 key cards
5♠ P ? asks for trump queen (a grand slam try)
5NT trump queen, no kings
6♣ trump queen, ♣K OR ♦K and ♠K
6♦ trump queen, ♦K OR ♣K and ♠K
6♥ no trump queen
7♥ trump queen and three kings
When we show 0/3 or 1/4 key cards, a return to the trump suit does not require the key-card responder to continue with the higher number of key cards if responder has already shown strength in the auction and it is clear that he must have the higher number.
At club level it is very unusual for the opponents to be bidding while you are conducting a slam auction, but in a stronger field you will find that the opponents will bid a lot and try to test your slam agreements. You need to be prepared.
If the interference consumes 2 bids or less, then Pass shows the first step of the response and Double/Redouble shows the second step.
4NT Bid ? Pass 1 or 4 key cards
Dbl/Rdbl 0 or 3 key cards
Step 1 2 key cards without key suit queen
Step 2 2 key cards with key suit queen
Higher bids show 3 key cards, key suit queen, and show first king not held
If the interference consumes more than 2 bids, use D-O-P-E and R-O-P-E. You remember this by Double/Redouble an Odd number, Pass shows an Even number.
4NT Bid ? Pass 0 or 2 key cards
Dbl/Rdbl 1 or 3 key card
Cheapest bid 4 key cards
In general returning to the trump suit is sign-off, pass is the next step asking for the trump queen if unknown and redouble being the second step asking for kings.
1♣ P 1♥ P Pass asks for the queen of hearts
4NT P 5♦ Dbl Redouble asks for kings
? 5♥ to play
5♠ asks for the king of spades
Occasionally opponents will double a cue bid in order to indicate a lead or potential sacrifice to their partner.
1♠ P 2♥ P Pass nothing to say (will wait for partner)
3♥ P 4♣ Dbl Redouble second round control
? 4♦ cue bid, denies club control
1♠ P 2♥ P
3♥ P 4♣ Dbl Redouble first round control
P P ? Other bids second round club control
If 4NT is needed as natural, it IS to be interpreted as natural.
4NT by either partner after a “4th suit force” is NAT. Similarly, after a “4th suit force” and NAT 2NT, 4NT by either partner is NAT.
In general to use RKCB, you need to set trumps either explicitly or implicitly.
1m 1M
2NT 4NT Natural. You must use checkback to set a suit to use RKCB.
1M 2m
2M 2NT
3NT 4NT Natural (quantitative).
1m 2NT
3NT 4NT Natural (quantitative).
1M 2m
2NT 3NT
4NT Natural (quantitative).
1M 2m
2NT 4NT Natural (quantitative).
(2m) DBL (Pass) 4NT Natural (quantitative).
(3m) DBL (Pass) 4NT Natural (quantitative).
(4m) DBL (Pass) 4NT Natural (quantitative).
(2M) DBL (Pass) 4NT Minors, distributional
(2M) DBL (4M) 4NT At least two suits (initially treated as minors)
(3M) DBL (Pass) 4NT At least two suits (initially treated as minors)
(4M) DBL (Pass) 4NT At least two suits (initially treated as minors)
1♣ (4♠) 4NT “Takeout” (D+C or D+H or “stronger” 5♥ bid)
(1♠) 2♣ (4♠) Pass
(Pass) DBL (Pass) 4NT Takeout
Provided no major suit is agreed, a bid of 5♠/NT has one of the following meanings unless part of another agreement.
When a suit has been agreed, a bid of 5♠ (5NT for spades) will be grand slam force asking for two of the top three honours.
After a major suit has been agreed at the 3-level, typically in a 2/1 auction, you must bid 3NT if you are not interested in slam, with four level bids showing serious interest.
After clear suit agreement, a bid of the next higher suit is key-card Blackwood ("Kickback") unless the suit has previously been bid naturally by the partnership. To be expanded.
When you want to make a slam try and have only one bid to do so below game, then that bid is defined as a random slam try. To be expanded.
An unnecessary jump to the five level is Exclusion Blackwood and asks for aces excluding the bid suit. Responses and continuations follow the same method as 3041 RKCB.
After pre-emptive openers, based on assumption that 4♣ could never usefully be natural so rather than cue bid, utilise it for more helpful enquiry. The exception of course over 3♣ where 4♦ is key-card and responses adjust accordingly
4♦ 0 key cards
4♥ 1 key card, no trump queen
4♠ 1 key card, with trump queen
4NT 2 key cards, no trump queen
5♣ 2 key cards, with trump queen
Continuations as per RKCB.