Exclusion Blackwood

Three things make a bid Exclusion Blackwood. A trump suit has been agreed. The bid is a jump in a new suit, to the five level or past four of the agreed major. And it cannot be a natural bid, a splinter or a control cue bid. It shows a void in the suit bid, slam interest, and asks partner for key cards.

The key cards are the usual five minus the ace of the void suit. That leaves four, the three other aces and the king of trumps. Partner answers in steps, starting with the first bid above the exclusion bid.

Partner never counts the ace of the void suit, even when they hold it. Kings and queens in that suit do not count either. The answers are ambiguous in the same way as in RKCB, and the auction almost always tells the asker which number it is. A limit raise cannot hold four key cards, for example.

Partnerships that play 3014 with RKCB usually swap the first two steps here as well. Agree it in advance.

The steps always start one bid above the exclusion bid, so the higher the void suit, the higher the answers. This table spells out the six common cases with a major agreed.

Look at where five of the trump suit falls in each row. Any answer below it leaves you room to sign off. Any answer above it puts you in slam whatever it shows. After 5♥ with spades agreed, only the first step lets you stop in 5♠, and a zero or three answer of 5NT already commits the partnership to six. So before you jump, picture the worst answer you could get and make sure you can live with it.

That is why the spade void over a heart fit is the comfortable case. The jump to 4♠ goes past 4♥, so it cannot be a splinter or a natural bid, and three of the four answers leave room for 5♥.

Once the asker knows the count, five of the trump suit is a sign-off if there is still room for it. The responder passes, unless they hold the higher of the two counts their answer showed. That rule is the same as in RKCB. Six of the trump suit is to play, and the asker may bid seven once every key card and the trump queen are known and thirteen tricks can be counted.

After a first or second step answer, the cheapest bid other than the trump suit asks for the trump queen. Partner returns to the trump suit without it. Holding the queen, partner bids a suit where they hold the king, or 5NT with no king to show. A king in the void suit is useless, so it is never shown. When the queen ask would carry the auction past five of trumps, most players skip it and judge the slam directly.

If an opponent doubles or overcalls the exclusion bid, partner answers with the same agreement you use over 4NT. DOPI and ROPI is the usual choice, and some pairs play DEPO instead.

Each hand below is played both ways. Plain RKCB gives a count that might include the useless ace, and Exclusion Blackwood takes that doubt away.

Finding a grand slam

Over 4NT, South would have answered 5♣, one key card. North, holding three, would know that one key card was missing, but not which. If it were the ♣A, the grand slam is laydown. If it were the ♦A, the grand slam would go down at once. North would have to stop in six. The exclusion bid removed the ♣A from the count, and with it the guess.

Bidding a small slam that 4NT stops short of

Over 4NT, South would also show one key card. North would then see two of the five missing without knowing that one of them is the ♠A, which is worth nothing opposite the void. Most players would sign off in 5♥. Yet 6♥ is a good slam, with twelve tricks from five hearts, three diamonds and a diamond ruff in dummy, two clubs once the ♣A has gone, and a spade trick after the ♠K forces out the ace.

• Using it without a trump suit. Exclusion Blackwood needs an agreed fit. Without one, a five-level jump in a new suit is anybody's guess.
• Confusing it with a cue bid or a splinter. After 1♠ 3♠, a bid of 4♣ is a control cue bid, and over 1♠ a direct jump to 4♣ by responder is a splinter. Only the jump to 5♣ is exclusion. Some partnerships also treat jumps after interference differently, so discuss it.
• Counting the ace of the void suit. It is the one card the asker told you to ignore. Holding it, answer as if you did not.
• Jumping when the worst answer is too high. If a zero answer would land above five of trumps, you are committed to slam opposite nothing. Cue-bid instead, or settle for game.
• Using it with a void partner has bid. Partner's high cards in their own suit may still be useful for discards or ruffs, and the ace there is a fair question. Plain RKCB often serves better.