User:Brian/Bridge/Responding to Blackwood
When partner has bid 4NT and according to your partnership agreements, your partner's 4NT bid means Blackwood, you must first remember which suit has been agreed upon as trumps, then respond to show how many keycards you hold. There are five keycards in total: the four aces, and the king of trumps.
Figuring out which suit is the trump suit
If you opened with notrump, make sure the 4NT bid is not a quantitative raise. If it's a quantitative raise, then it's not Blackwood!
If suit agreement has already been established, the agreed suit is the trump suit your partner is asking about. You need to know which suit is trumps so you know which suit's king to count when you make your response.
- If partner bid a suit and you supported it by bidding the same suit, then that suit is trumps. The same goes if you bid a suit and partner supported it.
- If you or your partner bid a suit and the other made a conventional raise, then that suit is trumps. For example, if your partner opened 1♥ and you responded with Jacoby 2NT, then hearts are trumps. If you opened 1♠ and partner responded 4♦—a splinter—then spades was agreed as trumps.
- If suit agreement was established by the initiation of control bidding by either you or your partner, then the suit previously agreed is still the trump suit.
- If agreement has not been shown, double-check that 4NT isn't quantitative before proceeding! It's quantitative if you opened notrump. (2♣ - 2♦ - 2NT and 2♣ - 2♦ - 3NT count as opening notrump.)
- If agreement has not been shown, but you're sure that 4NT is, in fact, Blackwood, then partner is implicitly agreeing with the last bid suit.
Responses to Blackwood
I have 0 or 3 keycards → Respond 5♦.
I have 1 or 4 keycards → Respond 5♣.
I have 2 or 5 keycards, but not the queen of trumps → Respond 5♥.
I have 2 or 5 keycards as well as the queen of trumps → Respond 5♠.
If partner rebids the trump suit, it is a sign-off. Pass.
If partner bids the next step up, but below 5 of the trump suit, it is a queen ask.
If partner bids 5NT, it is a king ask.
If partner bids 7NT, hopefully the meaning is obvious.