Blackwood

Blackwood is the most well-recognized convention for slam bidding. When a player is interested in slam but afraid of missing two aces, and hence two tricks, he can bid 4NT to ask his partner how many aces he holds. The responses to 4NT are:

Response	Meaning
5	0 or 4 aces
5	1 ace
5	2 aces
5	3 aces

All of the rebids made by the Blackwood bidder are natural, with the exception of 5NT. If the Blackwood bidder is contemplating a grand slam and needs to know how many kings his partner has, he can rebid 5NT. The responses to 5NT are:

Response	Meaning
6	0 or 4 kings
6	1 king
6	2 kings
6	3 kings

There are a number of ways to show aces if 4NT is overcalled.

One method is DOPI, which stands for "Double = Zero aces, Pass = 1." The cheapest available bid shows two aces, the second-cheapest bid shows three aces, and the third-cheapest bid shows four.

Another method of showing aces is DEPO, which stands for "Double = Even number of aces, Pass = Odd number of aces."

On occasion, the responder to a Blackwood inquiry will have a void somewhere in his hand. Voids should not be treated as aces; how they are treated instead is up to partnership agreement. A relative common approach is as follows.

Response	Meaning
6 of a side suit	1 ace and a void in the bid suit. The suit must be lower than the agreed trump suit.
6 of the agreed trump suit	1 ace and a void in a higher-ranking side suit.
5NT	2 aces and a void.

First, Blackwood shouldn't be used with a void. For example:

K5 AK9642 KQ873 —

West 1 3 North Pass Pass East 2 ? South Pass

In this sequence, East should cue-bid her club void rather than bid 4NT. The potential pitfall with Blackwood is that it would be impossible to distinguish the minor suit aces in West's response. In this auction East clearly cares more about the A than the A.

Second, Blackwood should only be used if you can handle any response. Here's a cautionary example from the late Ely Culbertson¹:

Q6 5 AQJ3 KQJT95

South 1 4 West 2 Pass North 3 ? East Pass

"If South holds two Aces, a small slam can undoubtedly be made in clubs. North would like to bid four notrump and find out. But if South has only one Ace his response to four notrump must be five diamonds. North cannot pass (for South may not have a diamond suit); and North cannot successfully bid six clubs (for the opponents have two Aces). So North must not bid four notrump. Instead he bids four diamonds and hopes South is strong enough to make the four-notrump slam try."

And finally... Blackwood should also be used only if partner's "ace count" will specifically indicate if a slam is achievable. From expert Larry Cohen:²

"If you have a side suit where you could be off the first two tricks (such as Qxx, or Jx), you shouldn't use Blackwood. For example, Opener holds:"

AKJ7642
AKQ
32
3

"You open 1 and partner makes a limit raise to 3.... [But] this is not a Blackwood hand. Let's suppose you use Blackwood and partner shows 1 ace. Now what?"

4NT should not always be interpreted as Blackwood. Expert Richard Pavicek offers this general playable rule:²

4NT is Blackwood if your side has never bid notrump naturally or if a major suit is agreed. Exception: An overcall of 4NT after an enemy bid is a special case (it is for takeout).

Here are some example auctions to consider.

The quantitative invitation to 6NT

West     Pass

North     1NT

East     Pass

South     4NT

South's 4NT shows a good balanced hand and invites North to carry on to 6NT with a maximum.

West     Pass

North     2NT

East     Pass

South     4NT

Ditto.

West     Pass Pass

North     2 2NT

East     Pass Pass

South     2 4NT

The same principle applies if North starts with an artificial 2 and rebids no-trumps.

4NT for takeout

West     1

North     4NT

East

South

Depending on partnership agreement, this can be played as a highly distributional Unusual No-Trump, asking partner to choose a minor.

West     4

North     4NT

East

South

Over an enemy 4/ opening bid, a 4NT overcall can be treated as takeout. The exact takeout suits are up for partnership discussion. For instance, 4NT can be takeout for any suit, or for the minors only.

Blackwood gets its name from its inventor Easley Blackwood, the late American player and writer.

1. Culbertson, Ely. Contract Bridge Self-Teacher. London, Faber and Faber, 1960.
2. Cohen, Larry. Slam Bidding — General.
3. Pavlicek, Richard. Notrump Slam Bidding.