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.[1]
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.[2]
The Culbertson 4-5 has been superseded by Blackwood and other conventions, but was reported in 1967 to still be popular among some leading British players.[5]