Culbertson 4-5 notrump
The Culbertson 4-5 notrump is a slam seeking convention in the game of contract bridge. It was devised in the early 1930s by Ely Culbertson. Most four-notrump conventions (Blackwood and its variants being the best known) demand that bidder's partner define their hand using agreed codified responses. In contrast, the Culbertson 4-5 describes the bidder's hand, and invites partner to use their judgement in the light of that information. Description. A bid of four notrump (subject to common-sense defined exceptions) shows either: In response: If the four notrump bidder next  bids five notrump, that shows all four aces. A bid of five notrump not preceded by four notrump shows three aces and the king of a bid suit. In subsequent bidding, common-sense rules apply. History. Culbertson's proposal of this convention threatened to disrupt the publication of the 1935 version of the Laws of Contract Bridge. The Portland Club, guardian of the laws in England, considered it equivalent to playing with exposed cards. Noel Mobbs persuaded the Club that they were wrong. In his 1949 book "Design for Bidding", "Skid" Simon called the Culbertson 4-5 "an adult weapon  and Blackwood merely a nice toy". The Culbertson 4-5 has been superseded by Blackwood and other conventions, but was reported in 1967 to still be popular among some leading British players.