A natural system is a bidding system which is mainly composed of natural calls. Natural systems are classified as green sticker by WBF. Examples of natural systems still in widespread use include:
The classical natural system refers to the Culbertson system and the Goren system, developed between 1930 to 1950. Their main features are:
- 4-card majors
- strong two bids
- strong jump shifts
- game forcing double raises
Many of the above aspects are now replaced by improved treatments and/or conventions.
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