Blackwood convention

Note: The Blackwood convention is used to determine the number of aces held by the bidder's partner. The bidder uses four no-trump as an asking bid, and the bidder's partner then responds in various ways depending on how many aces he or she holds, with five clubs indicating zero or four aces, five diamonds indicating one ace, five hearts indicating two, and five spades indicating 3. Further bids may then be used to determine the number of kings in the partner's hand.