Historic system of bidding devised and popularized by Ely Culbertson, first published in the Blue Book in 1933 and later revised in further Blue Books. Many of the features of the Culbertson system have provided a basis for modern methods. The very successful Four Aces team and public opinion influenced the system, leading to the publication of the Gold Book in 1936, which became standard in America for nearly fifteen years.
Features of the system were:
1. Valuation by Honour Tricks.
2. Uniform standards for biddable suits.
3. The approach forcing principle.
4. The forcing Two bids.
5. The forcing take-out (now known as a jump shift) showing three Honour Tricks.
6. Strong no-trump.
7. Non-forcing jump rebids by opener unless in a new suit.
8. Asking bids.