Standard Blackwood
When this convention is in force, a bid of 4NT asks the partner to provide information on the number of aces in his or her hand (as long as the previous bid is not 1NT, 2NT, or 3NT).
- With no aces, 5
- with one ace, 5
- with two aces, 5
- with three aces, 5
The asking bidder usually has one or two aces, so it is easy to discover the partnership's combined assets.
A continuing bid of 5NT asks for kings with the replies following the same pattern. However, asking for kings tends to confirm that your partnership has all the aces and the responder may simply bid the slam at the seven level if he has an appropriate hand.
The responder should not count a void as an ace. Eddie Kantar recommends bidding the void suit at the 6 level with three aces and a void and 5NT with two aces and a void.
Although alternatives to the Blackwood convention exist virtually all bridge partnerships deploy a variant of the Blackwood convention as part of their slam investigation methods.