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Control bids are used to explore for stoppers to see if slam can be bid. Ace asking bids, such as 4NT, should not be used when one of your suits has two quick losers (e.g.: xx) and your partner has not indicated control of the suit, nor when you have 1+ suit unstopped and a void since if your partner shows one control, you won't know if it is for the void suit or the one with 2+ losers.
An exception to the latter is the Exclusion Blackwood convention where instead of bidding 4N, you bid your void at a high level. (See the link for alternatives.).
Ace and void are first-round controls. Kx and singleton are second-round controls.
Control Bid format is shown in the box at the bottom of BidBase Editor.
In the Feb. 2018 Bulletin, p. 63, Billy Miller says:
My cuebids ["control bids"] are first- OR second-round controls, not just first-round controls.
On bidding that goes 1 -1 , 3-4, the 4 shows a control in diamonds and denies a control in clubs because controls are shown up the line.
Given the lack of space after 4, I believe that 4 should show nothing more than a club control. In fact, anything other than 4 would also show a club control.
The above is fairly standard, but other sources vary widely in how to make control bids:
- SantaCruzBridge.org says:
- The first control bid of a suit shows A or K and subsequent round control bids may show a singleton/void. [That is very much a minority view. Most experts say that a control bid can show either A/K or shortness, as said by Billy MIller above.]
- ACBLUnit390.org says:
- When a suit has been bid and raised and a game force situation exists, a new suit is a control bid.
[This conflicts with Miller's example, above, and Larry Cohen's, below, who both have control bids after an invitational raise, not a game force.]
- Shortness in a suit where partner has shown length of 4+ is not shown at the first chance to do so.
[For example, West opens 1 and N-S's bidding continues 2 -2, 4. Then a bid of 5 shows A/K, not shortness while a bid of 5 can be either A/K or shortness.]
- Control bids below game do not promise extra values but a 4N or 5N bid in the midst of a control bidding sequence does show extra values and asks partner to show extras.
[But then you cannot use 4N to ask for Aces/Key Cards as is commonly done once partner has shown control of your "xx" suit. Also, this site does not say how a player would respond to 4N to "show extras."]
- Second round controls are not shown above 4N unless first round control of the suit has been shown by the partnership.
[If, say, 4 is a control bid, it can be based on either first or second round controls (per this web site as well as Miller), so it's hard to know how first round control can have absolutely been shown by the partnership.]
- At the first available opportunity to cue-bid in a suit, we do not control bid a short suit control. Thus if this suit is bypassed the first time around it denies first or second round honor control of the suit [but not shortness].
[This is contradicted by Larry Cohen, below.]
- Larry Cohen:
- You open 1 and partner bids 3 (invitational). You "control-bid" 4, to show that you are interested in slam, and have a club control. In this case, your "control" is a singleton.
- Above 3-of-your-major, once a suit has been agreed, a new suit is a control-bid (ace, king, void, or singleton).
- Never jump into a control bid.
- Highly recommend Italian Style control bidding.
- AdvinBridge.com:
- American Style: First round controls are all shown first, then second round controls.
- Italian Style: Controls bids can be based on either first or second round controls.
The advantage is that if a suit in which you have 2 quick losers is skipped, you know immediately to sign off.
- Modern Style:
- Show Aces or voids in unbid suit(s).
- Show Aces only in our own side suits of 4+ cards.
- Show Aces or Kings in partner's suit(s), but not shortness.
- Nov. 2023, ACBL Bulletin Bidding Box, p.44, #5:
Other Notes:
Saying that controlled suits are bid "up the line" does not make it clear that after 1-1, 3, a bid of 3 is the lowest control bid you can make, so it would be made before, say, 4, even though clubs is the lowest ranking suit.
Often when you have a "xx" (2-quick losers) type of suit and thus cannot use 4N Ace Asking, you use control bidding and if partner shows a control in your "xx" suit, then you can switch from control bidding to 4N to ask for Aces or key cards.
After 1-1, 3, a bid of 4 is a control bid, not a raise of partner's suit.
After 1-2, 3, a bid of 3 is a delayed raise of partner's suit, not a control bid.(?)
Billy Miller's statement that 4 denies a club control raises this possible problem:
Say that you have xx, A... and A... After bidding of 1-1, 3, if you bid 4, you are denying the A, but if you bid 4, partner may bid 4 to show a diamond control and you still don't know about hearts. Presumably, you would then have to bid 5, but then that implies a second-round diamond control and also takes you past 4N. BidBase plays that the first control bid does not deny a control in lower suits but is asking about the next higher non-trump suit.]
More about control bidding.
In the BidBase Editor, the hand specifications for a control bid of a suit can be something like
"Num: 2+,<2 - Points: A/K".
This translates as follow:
Does the suit have 2 or more cards?
If so, does it have the A or K?
If so, then control bid the suit.
If the suit's length = 0 or 1, then control bid the suit.
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