Blackwood Convention: How 4NT Asks for Aces

Blackwood is a 4NT bid that asks partner how many aces he holds. Partner answers 5♣ with zero or four, 5♦ with one, 5♥ with two and 5♠ with three, and the asker then decides whether to bid a slam.

Easley Blackwood published the idea in 1933, and it is still the first slam convention most players learn. It belongs to every natural bidding system: 2/1 Game Force, SAYC and Acol all include it. Most tournament players now use the key card version, Roman Key Card Blackwood, but the plain ace-asking form is still common in club games, and it is the base everything else is built on.

Once your side has found a fit and has enough strength for slam, one player bids 4NT. Partner answers by steps:

The 5♣ answer covers both zero and four because the asker can always tell which: if you hold one or more aces yourself, partner cannot have all four, and if you hold none, a hand that has bid strongly will not have zero.

The asker is the captain. Partner gives the answer and then stays out of the way. Whatever the asker bids next is his decision, and partner passes unless asked another question.

Use 4NT when three things are true:

1. You know the trump suit, or you have a long, solid suit of your own.
2. Your side has slam strength: about 33 HCP for a balanced slam, or less when you have a good fit and some shortness. A slam bidding guide covers the evaluation side.
3. The only thing that can beat you is missing aces. You have every side suit covered by at least a king or a shortness, so the defenders cannot take two fast tricks in one suit.

Point three is the one players forget. Blackwood counts aces, not controls in a particular suit. If you hold two small cards in a suit nobody has bid, partner can show two aces and the defenders can still cash the ace and king of your weak suit. In that case use control-showing cue bids first.

Do not use Blackwood with a void either. Partner's answer will not tell you whether his ace is in your void suit, where it is wasted. Exclusion Blackwood exists for exactly that hand.

Be careful when clubs are trumps. If partner answers 5♥ or 5♠, you are already past 5♣. With clubs agreed and a hand that might be missing two aces, ask with a different tool, or only use 4NT when you can stand any answer.

Not every 4NT bid asks for aces. The most important exception:

• 4NT directly over a natural notrump bid is quantitative. After 1NT - 4NT or 2NT - 4NT, responder is not asking for aces. He is inviting 6NT, and opener passes with a minimum or bids 6NT with a maximum (see what 4NT over 1NT means in every system). The same applies to 1♦ - 1♠ - 2NT - 4NT, where no suit has been agreed. To ask for aces over a notrump opening, use Gerber.

Other common exceptions:

• 4NT over an opponent's preempt is often takeout, for example 4♠ by the opponents and 4NT by you: a two-suiter, usually the minors.
• 4NT as a sign-off. After a 4♣ Gerber ask and its answer, 4NT is usually to play.
• 4NT as a natural bid in competition, when the auction has been about which game to play rather than slam.

A safe partnership rule: 4NT is Blackwood when a suit has been agreed, or when the 4NT bidder has jumped there after his own strong suit bid. When partner's last bid was natural notrump and nothing is agreed, it is quantitative.

Missing two aces: sign off in five of your trump suit. If partner's answer was already above five of trumps, you are in trouble: that is why you think about the response levels before you bid 4NT.

Missing one ace: bid six of your trump suit, or 6NT if you want to play in notrump.

All the aces: you can try for a grand slam with 5NT, which asks for kings. Bidding 5NT promises that your side holds all four aces, so partner knows a grand slam is possible. The answers follow the same pattern one level higher:

Some partnerships treat 6♣ as zero or four, matching the ace answers. With extra tricks, such as a long running suit, partner may jump straight to seven instead of showing kings.

Example 1: slam with one ace missing. You are South and open 1♠ with a strong hand: ♠KQJ97, ♥A, ♦KQJ6, ♣K52. Partner gives a limit raise to 3♠ (10-12 points, four trumps). You now know the fit and the strength. Your singleton heart is the ace, and the other suits are all covered. The only question is aces, so you bid 4NT (see what 4NT means in every system).

Partner's two aces are the ♠A and the ♦A. Declarer loses only the ♣A: five spade tricks, the ♥A, four diamonds, the ♣K and a club ruff in dummy add up to twelve. Combined strength is just 29 HCP, but the fit and the singleton make the slam a good one.

Example 2: stopping in time. Same opening and raise, but now partner has the ♠A and the ♥K instead of the ♦A. He answers 5♦, one ace. Two aces are missing, so you sign off in 5♠. Partner must pass: the asker has decided.

1. Bidding Blackwood to find out whether slam is possible. Blackwood does not measure strength. Decide first that your side has slam values, then ask.
2. Asking with a void. Partner's ace may be in your void. Use Exclusion Blackwood or cue bids.
3. Asking with two fast losers in a side suit. Two aces opposite will not stop the defense from cashing the ace and king of your weak suit.
4. Partner overriding the captain. The responder to 4NT answers and then passes the sign-off, even with extra values.
5. Treating quantitative 4NT as Blackwood. Over a natural notrump bid, 4NT invites 6NT.
6. Forgetting 5NT promises all the aces. If you bid 5NT to "look for a grand" with an ace missing, partner may bid seven with extra tricks.

When the opponents interfere over 4NT, most pairs use DOPI and ROPI: double shows zero aces and pass shows one, and so on up the line.

• Roman Key Card Blackwood (RKCB) counts the king of trumps as a fifth "ace" and also finds the trump queen. Most experienced players use it, in either the 1430 or the 3014 order. It solves the biggest weakness of plain Blackwood: reaching a slam missing an ace and the trump king.
• Roman Blackwood answers 5♣ with zero or three aces, 5♦ with one or four, and two aces with 5♥ or 5♠, where the choice between them says something about which two. Old-fashioned, but you may meet it.
• Gerber asks for aces with 4♣, mainly over notrump openings.
• Exclusion Blackwood asks for aces outside a void suit.

If you play with a regular partner, upgrade to RKCB. The extra information about the trump king and queen is worth far more than the small extra memory work.

Blackwood is simple to learn and easy to misuse, so the best practice is on full deals. In the BridgeDummy Bidding Room you bid random hands with EPBot robots and see all four hands at the end, so you learn when 4NT was the right question and when a cue bid would have been better. Our bidding puzzles score each candidate call over many deals that fit the auction, which shows how often a borderline slam really makes.

• Roman Key Card Blackwood: the modern version with the trump king and queen.
• Gerber convention: asking for aces over notrump.
• Slam bidding: how to tell when slam is worth trying.