The Blackwood Convention

Most failed slams do not go down because the partnership lacked points. They go down because the opponents cash two aces before declarer gets in. Two hands can hold 33 points between them and still be missing the ♠A and the ♥A.

The Blackwood convention is the oldest and simplest guard against that. Once you know where you want to play and that the strength for slam is there, you ask partner how many aces they hold, and you stay out of a slam that cannot make.

After a trump suit has been agreed, a bid of 4NT asks partner for aces. Partner answers in steps, starting with the cheapest bid: 5♣, 5♦, 5♥, 5♠. The player who bid 4NT is now the captain. They add partner's aces to their own, decide on the level, and place the contract. Partner follows that decision.

The 5♣ answer covers both zero and four aces. That sounds risky, but in practice the auction so far tells you which one it is. A partner who opened the bidding and then answers 5♣ opposite your strong hand with two aces cannot hold four of them.

Blackwood answers one question: how many aces are missing. It does not tell you whether the hands fit, whether partner has the king you need, or whether a suit is wide open. Use it only when that one answer is all you need to choose between game and slam.

• A trump suit is agreed, or clearly implied by the auction. 4NT with no fit in sight is a different bid (see below).
• The strength for slam is already there. Around 33 points between the two hands, or less with a long suit and a good fit. Blackwood is not a slam try. Use it only to check aces once you know the values are there.
• Every side suit is under control. If you hold two small cards in a suit nobody has bid, partner's ace count will not tell you whether the opponents can take the first two tricks there. Cue-bid instead.
• You do not hold a void. Partner will count an ace in your void suit, and that ace is worthless to you. With a void, cue-bid or agree to play Exclusion Blackwood.
• You can stand any answer. When clubs are trumps, a 5♥ or 5♠ reply has already carried you past 5♣. Ask with a club fit only if you know the answer cannot put you overboard.

When 4NT is not Blackwood

When 4NT raises a natural notrump bid directly, as in 1NT - 4NT or 2NT - 4NT, it is quantitative: an invitation to 6NT, not an ace ask. Partner passes with a minimum and bids slam with a maximum. To ask for aces over a notrump opening, use Gerber, the jump to 4♣. In some competitive auctions 4NT is also natural or shows two suits. Everywhere else, once a suit is agreed, the default is Blackwood.

Once partner has answered, the captain has three choices.

1. 1.Sign off in five of the trump suit when two aces are missing. Partner must pass.
2. 2.Bid the small slam when no more than one ace is missing.
3. 3.Bid 5NT when the partnership holds all four aces and a grand slam is possible. 5NT asks for kings with the same step answers, starting at 6♣. Because it promises every ace, partner may jump straight to seven with extra tricks the captain cannot know about.

In Blackwood, 5NT is always the king ask and never a way to stop in notrump. If you want to play in 5NT, most partnerships use a bid of an unbid suit at the five level to ask partner to bid 5NT, which the captain then passes. Agree this before you need it.

In the first deal North opens 1♠ and South makes a limit raise to 3♠, showing four-card support and about 10 to 12 points.

The second deal shows Blackwood keeping you out of a bad slam. North holds ♠KQ ♥KQJ1074 ♦KQJ ♣A5, 21 HCP with a strong six-card heart suit. South raises 1♥ to 3♥ with ♠J852 ♥A963 ♦74 ♣KQ3. North bids 4NT and hears 5♦, showing one ace. North has only the ♣A, so the ♠A and ♦A are both missing. North signs off in 5♥ and South passes. Eleven tricks are there, but a slam would lose the first two.

• Asking with a weak side suit. With two small cards in an unbid suit, a one-ace answer does not tell you whether the missing ace is there or whether the king is missing too.
• Asking with a void. Partner's ace in your void counts in the answer and takes no trick.
• Overruling the captain. When the 4NT bidder signs off, the responder passes, even with a maximum. The captain already knows how many aces you hold.
• Mistaking a quantitative 4NT for Blackwood, or the other way around. Over a natural notrump bid with no suit agreed, 4NT invites; it does not ask.
• Bidding 5NT without all four aces. It promises every ace and invites a grand slam. Partner is entitled to bid seven.
• Using Blackwood as a slam try. Find out whether slam is there first, with a strong raise such as Jacoby 2NT or a splinter, and use 4NT only to check controls.

Plain Blackwood treats the king of trumps like any other king, which is its biggest weakness. Missing an ace and the trump king is usually fatal, and plain Blackwood cannot tell you about it. Most tournament players now use Roman Key Card Blackwood, which counts the trump king as a fifth ace and can locate the trump queen. Plain Blackwood remains a good choice for new partnerships and casual games because it is easy to remember and hard to get wrong.

Two further agreements cover gaps in the basic version. DOPI and ROPI tell you how to answer when an opponent bids or doubles over your 4NT. Exclusion Blackwood, a jump to the five level in a suit where you hold a void, asks for aces outside that suit. Both are optional, so agree them with your partner before you use them.

What is the Blackwood convention in bridge?

Blackwood is a bid of 4NT that asks partner how many aces they hold, used once a trump suit is agreed and the strength for slam is there. Partner answers 5♣ with zero or four aces, 5♦ with one, 5♥ with two and 5♠ with three, and the 4NT bidder then decides whether to bid slam.

What are the responses to Blackwood 4NT?

Partner answers in steps: 5♣ shows zero or four aces, 5♦ one ace, 5♥ two aces and 5♠ three aces. The auction almost always makes clear whether 5♣ means zero or four.

What does 5NT mean after Blackwood?

It confirms that the partnership holds all four aces and asks how many kings partner has, with answers starting at 6♣ for none. It is a grand slam try, so it must not be used as a way to play in 5NT.

Is 4NT always Blackwood?

No. When 4NT raises partner's natural notrump bid, as in 1NT - 4NT, it is a quantitative invitation to 6NT. It is Blackwood when a trump suit has been agreed or is clearly implied.

Should I use Blackwood with a void?

Usually not. Partner will count an ace in your void suit, and that ace is wasted. Cue-bid instead, or use Exclusion Blackwood if your partnership plays it.

What is the difference between Blackwood and Roman Key Card Blackwood?

Blackwood counts the four aces. Roman Key Card Blackwood counts five key cards, the four aces plus the trump king, and can also ask about the trump queen. Most experienced partnerships play the key-card version.

What is Exclusion Blackwood?

Exclusion Blackwood is a jump to the five level in a suit where the asker holds a void, asking partner for aces outside that suit. The ace of the void suit is ignored, because it would take no trick. It is an optional agreement, so discuss it with your partner before you use it.