What is Jacoby rule?
The Jacoby rule is an addition to backgammon with the doubling cube. Under it, a gammon or a backgammon counts as an ordinary single win unless the cube has been turned at least once in the game. Once either player has doubled and the double was taken, gammons count two and backgammons three, times the cube, as usual.
The rule exists to speed up single games. Without it, a player far ahead might keep playing on for a gammon instead of doubling the opponent out, and long games of little doubt would drag on. With it, a player who wants the gammon has to turn the cube first, which gives the opponent the chance to pass and end the game.
The Jacoby rule only applies to single games with the doubling cube. In match play, gammons always count, so the table setup ignores it there.
Rule changes
| Rule | Standard Backgammon | Jacoby rule |
|---|---|---|
| Gammons and backgammons | Standard BackgammonAlways count two and three times the cube. | Jacoby ruleCount as a single win while the cube is still at 1; they count in full once the cube has been turned. |
| Doubling cube | Standard BackgammonOptional: can be turned on in the table setup. | Jacoby ruleRequired: the rule only makes sense with the cube, so it is played with the doubling cube on. |
| Match play | Standard BackgammonGammons count in every game of a match. | Jacoby ruleNot used in matches: there, gammons always count. |
History
The rule is named after Oswald Jacoby, an American bridge champion and one of the best-known backgammon writers of the 20th century. With John R. Crawford he wrote The Backgammon Book, published in 1970, which helped bring the modern game, cube and all, to a wide audience.
The Jacoby rule became standard in money play, in head-to-head games and in chouettes, where one player takes on a team, because it keeps games moving. It has never been used in matches, where gammons decide matches and players need every point they can win.