Culbertson system is the earliest notable natural bidding system. It has the following features: * 4-card majors * Strong (16-18) 1NT * Strong two bids * Strong jump shifts * Game-forcing jump raises * Strong jump overcalls * Culbertson 4-5NT * Culbertson asking bids It relied on honour trick strength first (it was created before the HCP scale), but later conformed to point count. Many of the features are now considered outdated and replaced by weak variants.