Forum Archive : Rules

Jacoby rule

From:   Daniel Murphy
Date:   5 December 1997
Subject:   Re: jacoby rule doubling

> Could somebody explain what the Jacoby rule is?

The Jacoby rule, invented  by Oswald Jacoby, says:

In money play, the game winner receives no extra credit for gammons or
backgammons unless the cube has been doubled at least once.

The Jacoby rule is standard for money play almost everywhere, although
it's still a good idea to establish that you're using the rule when
you start a money play session.

The sole purpose of the rule is to speed up the game -- add a little
more excitement  -- finish this game and move on to the next. The
Jacoby rule is never used in match play. The rule avoids those long
games where, having missed the market by a mile, one might play on
with little chance for either a gammon or a loss, or where, in match
play with a centered cube, a position is too good to double.

The Jacoby rule has some influence on both checker play and cube
decisions, mostly on checker play.

It encourages more aggressive checker play to achieve a gammonish
doubling position. The idea (simply put) is that if the strategy
works, you double and win four points; if it fails, you pass and lose
one, since unless the cube is turned you can't lose a gammon.

The rule's affect on cube decisions is harder to pin down. It seems
sensible that there will be positions which are not good enough to
double in a match but may be money doubles, if much of the doubler's
equity comes from gammons won, even if the doubler's overall winning
chances aren't terrific. In actual money play the rule probably
encourages typical players to double -- not just earlier -- but too
early, for fear of missing out on four points by not "activating
gammons." But against opponents who are known to be afraid to take a
double in a gammonish position, or to redouble if the game turns
around, the "early" double can still be a money winner.

Daniel Murphy
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