In the philosophy of language

Philosophy of language

Philosophy of language is the reasoned inquiry into the nature, origins, and usage of language. As a topic, the philosophy of language for analytic philosophers is concerned with four central problems: the nature of meaning, language use, language cognition, and the relationship between language...

 and modal logic

Modal logic

Modal logic is a type of formal logic that extends classical propositional and predicate logic to include operators expressing modality. Modals — words that express modalities — qualify a statement. For example, the statement "John is happy" might be qualified by saying that John is...

, a non-rigid designator (or flaccid designator) is a term that does not extensionally refer to the same object in all possible worlds

Possible Worlds

Possible Worlds may refer to:* Possible worlds, a concept in philosophy* Possible Worlds , by John Mighton** Possible Worlds , by Robert Lepage, based on the Mighton play* Possible Worlds , by Peter Porter...

. For example, consider the phrase "The 43rd president of the United States of America": while the 43rd president of the United States is actually George W. Bush

George W. Bush

George Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....

, if things had been different, it might have been Al Gore

Al Gore

Albert Arnold "Al" Gore, Jr. served as the 45th Vice President of the United States , under President Bill Clinton. He was the Democratic Party's nominee for President in the 2000 U.S. presidential election....

 or Ralph Nader

Ralph Nader

Ralph Nader is an American political activist, as well as an author, lecturer, and attorney. Areas of particular concern to Nader include consumer protection, humanitarianism, environmentalism, and democratic government....

 instead. (How remote these possible worlds are from the actual world is a discussion for physics

Many-worlds interpretation

The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an...

 and counterfactual

Counterfactual

Counterfactual may refer to:* Counterfactual conditional, a grammatical form * Counterfactual subjunctive, grammatical forms which in English are known as the past and pluperfect forms of the subjunctive mood* Counterfactual thinking* Counterfactual history* Alternate history, a literary genre*...

ism.) Non-rigid designators are defined by contrast with Saul Kripke

Saul Kripke

Saul Aaron Kripke is an American philosopher and logician. He is a professor emeritus at Princeton and teaches as a Distinguished Professor of Philosophy at the CUNY Graduate Center...

's notion of a rigid designator

Rigid designator

In modal logic and the philosophy of language, a term is said to be a rigid designator when it designates the same thing in all possible worlds in which that thing exists and does not designate anything else in those possible worlds in which that thing does not exist...

, which pick out the same thing uniquely in every possible world; while there are possible worlds in which the 43rd president of the United States is Al Gore instead of George W. Bush, there are no possible worlds where George W. Bush is anyone other than the man who, in fact, he is. (There are worlds where some person other than George W. Bush is named "George W. Bush," but that's neither here nor there.) Kripke uses this apparent asymmetry to argue (in Naming and Necessity

Naming and Necessity

Naming and Necessity is a book by the philosopher Saul Kripke that was first published in 1980 and deals with the debates of proper nouns in the philosophy of language. The book is based on a transcript of three lectures given at Princeton University in 1970...

) that no definite description

Definite description

A definite description is a denoting phrase in the form of "the X" where X is a noun-phrase or a singular common noun. The definite description is proper if X applies to a unique individual or object. For example: "the first person in space" and "the 42nd President of the United States of...

 (which can designate non-rigidly) can be the meaning of a proper name

Proper name

"A proper name [is] a word that answers the purpose of showing what thing it is that we are talking about" writes John Stuart Mill in A System of Logic , "but not of telling anything about it"...

.

It is worth noting that some philosophers, such as Gareth Evans

Gareth Evans (philosopher)

Gareth Evans was a British philosopher.-Life:Gareth Evans studied Philosophy, Politics and Economics at University College, Oxford . His philosophy tutor was Peter Strawson...

have expressed doubt as to whether non-rigid expressions ought to be called designators at all.