Blackwood If you have an agreed suit, you can find out how many Aces (and Kings) partner holds by using a 4NT bid. A reply of 5♣ shows 0 or 4, 5♦ shows 1, 5♥ shows 2 and 5♠ shows 3.

If your side has all four Aces, bidding 5NT will repeat the process for Kings.

The Replier can show one Ace plus a Void by bidding 6 of the Void suit if it ranks below the agreed trump, or 6 of the trump suit if the Void ranks above.
A Reply of 5NT shows two Aces plus a Void in some suit.

Gerber : Similar to Blackwood, this convention uses a 4♣ bid to initiate the Ace question, with 4♦ showing 0 or 4, 4♥ showing 1, 4♠ showing 2 and 4NT showing 3.

Not all 4♣ bids are Gerber, and deciding which ones are needs to be addressed by the partnership. For these Deals 4♣ is Gerber only when it follows a bid of 1NT or 2NT.

BakerBridge has complete lessons for these two conventions.

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