Most novice players will have heard of cue bidding, but many regard it as a foreign country - a remote region, full of mystery and danger. So let's explore - and familiarise ourselves with what is basically quite a simple idea.
WHAT IS CUE BIDDING?
Cue bidding is a means of slam exploration. Once a suit has been agreed (either explicitly or implicitly) a cue bid signifies the possession of a control in one of the other suits. The control may be an Ace or a King, or a singleton or a void. To put it another way, a cue bid tells partner that the opponents will not be able to cash an immediate two winners in this particular side suit.
HOW DO I RECOGNISE A CUE BID?
Where a trump suit has been explicitly agreed, a cue bid will be shown by a jump to another suit at the 3 level, or a bid of any new suit at the 4 level. Where a trump suit is agreed by inference (without explicit support other than via the cue bid itself), the cue bid will always involve a jump bid.
Here are some example of the first of these - a cue bid following explicit suit agreement (no opposition bidding):
1H - 3H - 4C* - with 4C being the cue bid; 1H - 2C - 2H - 3S* - with 3S being the cue bid; 1S - 2D - 3D - 4C* - with 4C being the cue bid.
Here are some examples of cue bidding where the trump suit is agreed by inference - in other words, by the cue bid itself (again, no opposition bidding)
1S - 2H - 4C* - hearts are (implicitly) agreed as trumps, with 4C being the cue bid; 1S - 2D - 2S - 4C* - spades are agreed as trumps, with 4C being the cue bid; 1D - 1H - 2D - 3S* - diamonds are agreed as trumps, with 3S being the cue bid
WHAT IS THE POINT OF CUE BIDDING?
The point of cue bidding is to help partner judge whether slam is a good proposition. It works by letting partner know that a given suit is 'controlled' - whatever else the defence can do, they cannot cash two immediate winners in this suit. Conversely - and this is just as important - if in the course of slam exploration a side suit is bypassed (not bid), this denies possession of a first or second round control in the bypassed suit, telling partner not to proceed further unless she can guard the suit in question. Cue bidding comes into its own when the partnership has exchanged sufficient information for them to know that slam is in prospect, bringing them to the point at which they need to assure themselves that no suit is vulnerable to immediate attack. This is not dissimilar to a Blackwood Ace/King enquiry, but the difference is that whereas Blackwood focusses upon the TOTAL number of Aces (and perhaps Kings), cue bidding focusses upon one suit at a time.
LET'S HAVE SOME EXAMPLES
AKxxx / Kxx / x / AKQx Qxxx / Ax / xxxx / xx
The bidding proceeds: 1S - 2S - 4C* - 4H* - 6S
Note the wonderfully helpful return cue bid of 4H. Responder is showing first or second round control, and opener will be confident that partner is showing the Ace. Also - responder has bypassed 4D - so no diamond control, which means no wasted values in the diamond suit. Opener might have followed this with a Roman Key Card enquiry, including establishing whether partner has the Queen of trumps - but she has a bus to catch and so leaps confidently to slam. Note that an immediate Blackwood enquiry would not have been nearly as helpful. Partner would show one Ace - but which one? If it's the Ace of diamonds slam may be a pipe dream.
One more example:
AK / AKQJxx / KJx / xx xxx / xxxx / Ax / QJxx
The bidding proceeds: 1H - 2H - 3S* - 4D* - 4H
Despite opener's fantastic hand, leading her to initiate cue bidding, she signs off in 4H. Why? Because she knows the partnership has two immediate losers in clubs. Her partner's return cue bid has told her this - partner's return cue bid of 4D having bypassed the club suit. That omission told a story - that the slam would go down on a club lead.