“Metalanguage: A language used to refer to statements made in another language, called in this context the object language. If the statements being referred to are in French and the statements referring to them are in English, for example, then the distinction between object language (French) and the metalanguage (English) is clear, but if the object language and metalanguage are both expressed in English, or both in a formal language such as the predicate calculus, then confusion can arise. Quotation marks can sometimes help, as in the sentence ‘Snow is white’ is true if an only if snow is white, in which the statement belonging to the object language is enclosed in quotation marks. Many paradoxes, including debatably the liar paradox, arise from a failure to distinguish object language from metalanguage: expressions involving true and false, when applied to a sentence, must always be expressed in a metalanguage and not in the object language of the sentence, The ideas behind the concept of a metalanguage are traceable to an article ‘On Denoting’ by the Welsh philosopher Bertrand (Arthur William) Russell (1872-1972) in the journal Mind in 1905, and the concept was fully developed by the Polish logician and mathematician Alfred Tarski (1902-1983) in his monograph De Wahrheitsbegriff in den formalisierten Sprachen (The Concept of Truth in Formalized Languages) in 1933.”
Excerpted from: Colman, Andrew M., ed. Oxford Dictionary of Psychology. New York: Oxford University Press, 2003.
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