# Principle of Restricted Choice

In contract bridge, the principle of restricted choice states that play of a particular card decreases the probability its player holds any equivalent card. For example, South leads a low spade, West plays a low one, North plays the queen, East wins with the king. The ace and king are equivalent cards; East's play of the king decreases the probability East holds the ace – and increases the probability West holds the ace. The principle helps other players infer the locations of unobserved equivalent cards such as that spade ace after observing the king. The increase or decrease in probability is an example of Bayesian updating as evidence accumulates and particular applications of restricted choice are similar to the Monty Hall problem.

Jeff Rubens (1964, 457) stated the principle thus: "The play of a card which may have been selected as a choice of equal plays increases the chance that the player started with a holding in which his choice was restricted." Crucially, it helps play "in situations which used to be thought of as guesswork." In many of those situations the rule derived from the principle is to play for split honors. After observing one equivalent card, that is, one should continue play as if two equivalents were split between the opposing players, so that there was no choice about which one to play. Whoever played the first one doesn't have the other one.

When the number of equivalent cards is greater than two, the principle is complicated because their equivalence may not be manifest. When one partner holds ♣Q and ♣10, say, and the other holds ♣J, it is usually true that those three cards are equivalent but the one who holds two of them does not know it. Restricted choice is always introduced in terms of two touching cards – consecutive ranks in the same suit, such as ♥QJ or ♦KQ – where equivalence is manifest.

If there is no reason to prefer a specific card (for example to signal to partner), a player holding two or more equivalent cards should sometimes randomize their order of play (see the note on Nash equilibrium). The probability calculations in coverage of restricted choice often take uniform randomization for granted but that is problematic.

The principle of restricted choice even applies to an opponent's choice of an opening lead from equivalent suits. See Kelsey & Glauert (1980).

Read more about Principle Of Restricted ChoiceExample, Better Calculation of Odds, Better Yet, Mathematic Theory

### Other articles related to "principle of restricted choice":

Principle Of Restricted Choice - Mathematic Theory
... The principle of restricted choice is an application of Bayes Law ... Increases and decreases in the probabilities of original lies of the opposing cards, as the play of the hand proceeds, are examples of Bayesian updating as evidence accumulates ...

### Famous quotes containing the words principle of, choice, principle and/or restricted:

In case I conk out, this is provisionally what I have to do: I must clarify obscurities; I must make clearer definite ideas or dissociations. I must find a verbal formula to combat the rise of brutality—the principle of order versus the split atom.
Ezra Pound (1885–1972)

The style of an author should be the image of his mind, but the choice and command of language is the fruit of exercise.
Edward Gibbon (1737–1794)

The principle of majority rule is the mildest form in which the force of numbers can be exercised. It is a pacific substitute for civil war in which the opposing armies are counted and the victory is awarded to the larger before any blood is shed. Except in the sacred tests of democracy and in the incantations of the orators, we hardly take the trouble to pretend that the rule of the majority is not at bottom a rule of force.
Walter Lippmann (1889–1974)

Growing up means letting go of the dearest megalomaniacal dreams of our childhood. Growing up means knowing they can’t be fulfilled. Growing up means gaining the wisdom and skills to get what we want within the limitations imposed by reality—a reality which consists of diminished powers, restricted freedoms and, with the people we love, imperfect connections.
Judith Viorst (20th century)