# Backgammon: Jacoby rule with doubling cube?

As per my understanding of Jacoby rule will be applied when doubling cube is not used during the game.

If I select Jacoby rule for the game and If either of the players uses the cube, Will Jacoby rule will not be applied at the end of the game? Or Are players not able to use doubling cube if Jacoby is selected at the start of a game?

Ref: http://www.bkgm.com/gloss/lookup.cgi?jacoby+rule I have used this site for the Jacoby rule.

If any one has some better explanation or ref. link, please provide

• I couldn't tell by the title if this was a Magic the Gathering question, or a bridge question. Imagine my surprise... Aug 2, 2017 at 14:08
• @steenbergh: It's my feeling too, that names of games should be in the title (unless it's obvious; who would think of "32 houses and 12 hotels" as something other than Monopoly.).boardgames.meta.stackexchange.com/questions/21/… Aug 8, 2017 at 0:56
• Updated the name to give more clarity about the question Aug 8, 2017 at 4:41

The rule (as in the link):

A rule popular in money play which says that gammons and backgammons count only as a single game if neither player has offered a double during the game.

Probably the better way to say it is: If neither player has offered a double during the game, gammons and backgammons do not count.

This doesn't turn off the doubling cube, it just means that if you or your opponent don't double, the best you're doing is a single. Once the cube has been offered and accepted for the first time, gammons will count, and the normal range of 2-6 points is on the table.

(In theory, this means that every game will have at least 1 double offered, since this rule removes the potential of a position being "too good to double" before the cube is turned for the first time.)

The Jacoby rule is a "house rule" used in most money games that encourage people to turn the cube early, by penalizing players that turn the cube "too late."

A doubling (and acceptance) voids the Jacoby rule. If the double is made and accepted, this is called "doubling in" (the opponent). If the double is declined, the result is "doubling out" (of the opponent), at which point gammon/backgammon equity becomes moot.

The Jacoby rule applies only if the cube is not turned. Then it means that no gammons or backgammons are scored, only single games,because the cube hasn't been turned. This "not scored" applies even if a gammon or backgammon is actually achieved on the board.

The purpose of the rule is to encourage people to turn the cube early enough to double their opponents "in" if they want to get the extra points for gammons and backgammons. If they wait, they always have the option of doubling the opponents "out," but such play is now rendered inferior.

What the rule does is that it takes away the "fallback" position of "Oh, I forgot to double but I can still win a gammon or backgammon if I don't turn the cube now." (That is what another poster meant by a position being "too good to double.") Because that is specifically what the Jacoby rule prohibits. This prohibition makes waiting to double opponents "out" a "second best" choice.

• That is incorrect - the purpose is (as noted above by @J. John) to remove the circumstance where a (single value) game position becomes too good to double. Jacoby Rule Aug 7, 2017 at 22:53
• @ForgetIwaseverhere: Put another way, you must double the person in" if you want the gammon/backgammon equity under the Jacoby rule. if the position is "too good to double," you always have the option of doubling the person "out," but you have lost the option of doubling him "in" (unless he is a fool, in which case it becomes what I call a "superinvestment double.") Aug 7, 2017 at 23:48
• That is really poor play - if your equity in the game is currently above, or even well above, 1.0, then why settle for only 1.0? There are end-game positions where one doubles as insurance (doubling the opponent out as you say). but good doubles in the early and mid-game are made when the opponent's best option is to accept.- thus actually doubling one's equity in the game. Aug 8, 2017 at 0:07
• @ForgetIwaseverhere: The Jacoby rule doesn't actually forbid people waiting to double. It just discourages such inferior play by taking away a key benefit of waiting (vs. "tournament" play), thereby making it a "second best choice.". Which is the point I made in my revision. Aug 11, 2017 at 2:27