Practice on Cuebids
Practice hands where the partnership has slam values and needs to decide whether to investigate or stop in game.
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Systems
Last updated
2026-08-01
What is Blackwood?
Blackwood is a 4NT bid that asks partner for aces. It helps a partnership avoid slams missing too many aces.
Devised by Easley Blackwood in the 1930s, it is one of the oldest and best-known slam conventions, and its descendants remain standard today.
Classic responses are step-based, showing zero, one, two, three, or four aces depending on the version used.
4NT asks for aces
- After a spade fit is agreed, 4NT is normally Blackwood or key-card Blackwood.
When not to use it
Blackwood is poor when a side suit might have two quick losers. It reports the ace count, but it does not reveal whether the opponents can cash the first two tricks.
- Do not ask when the partnership may be off the ace and king in a side suit.
- Do not ask without knowing the trump suit or final strain.
- Use control bidding first when side-suit safety is unclear.
Responses and follow-ups
In classic Blackwood, the usual step responses to 4NT are 5 for zero or four aces, 5 for one ace, 5 for two aces, and 5 for three aces. Some pairs reverse or modernize this structure, so a firm agreement is essential.
After hearing the ace count, the asker places the contract. When five of the agreed trump suit is still available, that bid is normally a signoff. If the response has bypassed it, especially with a minor as trumps, the partnership needs an agreed escape and the asker must have been prepared for that answer.
A continuation of 5NT asks for kings and, in the traditional rule, guarantees that the partnership holds all four aces, so it is only bid when a grand slam is in the picture. One established treatment uses five distinct replies: 6 shows no kings, 6 one, 6 two, 6 three, and 6NT all four. The SAYC version of Standard American and many Acol methods instead mirror the ace scale, with 6 showing zero or four kings, followed by one, two, and three in ascending steps. The partnership must agree which king scale applies.
- Before asking, decide whether the partnership can survive every possible answer.
- When the asker has a void, ordinary Blackwood cannot reveal whether partner's ace is wasted in that suit; use control bidding or Exclusion Blackwood instead.
- Void-showing responses solve a different problem by describing a void in responder's hand.
- If 4NT could be quantitative in the auction, agree whether a prior suit bid or fit establishes Blackwood.
- If the opponents bid over 4NT, the normal steps no longer apply; most pairs agree a scheme such as DOPI or DEPO for these auctions.
Signing off after the answer
- 5 showed one ace, so the partnership may be missing two aces.
- Five of the agreed trump suit is a sign-off; responder should pass.
5NT asks for kings
- 5 showed two aces; with the other two in the asker's hand, all four are accounted for.
- 5NT now asks for kings and invites a grand slam. Replies follow the agreed king scale starting with 6.
Blackwood examples
Classic Blackwood is a blunt tool. These auctions show when it answers the right question and when another slam tool would be safer.
Schematic ace-count sequence
- Responder 5 shows one ace in a common classic scale.
- This sequence illustrates the response mechanics only. The jump to 6 is justified only if the asker's own aces and side-suit controls make slam safe.
Do not ask with two quick losers
- If the asker has a side suit like Qxx opposite unknown values, 4NT may not reveal two quick losers.
- Control bidding is usually better before asking for aces.
Quantitative not Blackwood
- In many notrump auctions, 4NT asks partner to bid slam with a maximum.
- This is not classic Blackwood unless the partnership explicitly says so.
Every side suit controlled: ask away
- After 1 and a limit raise to 3, the question is whether responder holds either missing ace; the side-suit kings prevent two quick losers when exactly one ace is missing.
- Bid 4NT: over 5 showing one ace, bid 6; over 5 showing none, sign off in 5.
Two fast diamond losers: do not ask
- After 1 and a limit raise to 3, 4NT is wrong: partner could show one ace and slam might still lose the first two diamond tricks.
- Control bid 3 instead and give up on slam if partner cannot show a diamond control.
Before bidding 4NT
A useful Blackwood habit is pausing before the ask. The asker should confirm that the trump suit is known, every possible answer leaves a safe landing spot, and side-suit controls have already been handled.
- Use Blackwood to avoid missing aces, not to discover whether slam is generally good.
- Do not ask when partner's answer may force the partnership above a safe contract.
Common mistakes
- Using Blackwood before agreeing a trump suit.
- Asking for aces when a side suit has two possible quick losers.
- Confusing classic Blackwood responses with Roman Key Card Blackwood responses.
FAQ
Is 4NT always Blackwood?
No. In many auctions 4NT can be quantitative or natural. Context and partnership agreement decide.
Should modern pairs play Blackwood or RKCB?
Many modern pairs prefer Roman Key Card Blackwood because the trump king is nearly as important as an ace once trumps are agreed. Classic Blackwood remains playable; the partnership must agree which response structure applies.