Extensionalism, in the
philosophy of language In analytic philosophy, philosophy of language investigates the nature of language and the relations between language, language users, and the world. Investigations may include inquiry into the nature of Meaning (philosophy of language), meanin ...
, in
logic Logic is the study of correct reasoning. It includes both Mathematical logic, formal and informal logic. Formal logic is the science of Validity (logic), deductively valid inferences or of logical truths. It is a formal science investigating h ...
semantics Semantics (from grc, wikt:σημαντικός, σημαντικός ''sēmantikós'', "significant") is the study of reference, Meaning (philosophy), meaning, or truth. The term can be used to refer to subfields of several distinct discipline ...
, is the view that all languages or at least all scientific languages should be extensional. It has been described as the default option for the scientism in the nineteenth century and the result of the application of empiricistic inductive methodology to the problem of semantics.


The idea of extensionality is considered a form of reductionism with the way it holds that every meaningful and declarative sentence is equivalent to some extensional sentence.
Rudolf Carnap Rudolf Carnap (; ; 18 May 1891 – 14 September 1970) was a German-language philosopher who was active in Europe before 1935 and in the United States thereafter. He was a major member of the Vienna Circle and an advocate of logical positivism. He ...
(in his earlier work) and
Willard Van Orman Quine Willard Van Orman Quine (; known to his friends as "Van"; June 25, 1908 – December 25, 2000) was an American philosopher and logician in the analytic philosophy, analytic tradition, recognized as "one of the most influential philosophers of the ...
were prominent proponents of this view. Carnap's thesis of extensionality is associated with the relation between extensional and nonextensional languages. According to the thinker, the former has simpler structures and constitutive rules than the latter so that it is possible to discuss exhaustively all scientific phenomena when using extensional language. The idea put forward by
Richard Montague Richard Merritt Montague (September 20, 1930 – March 7, 1971) was an American mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians ...
that the intension of a predicate or a sentence is identifiable from possible worlds to extensions is also attributed to Carnap. Quine, who maintained that he is a "confirmed extensionalist" maintained that an extensional language is one that contains no expressions that lead to non-extensionaal contexts. The early philosophy of
Ludwig Wittgenstein Ludwig Josef Johann Wittgenstein ( ; ; 26 April 1889 – 29 April 1951) was an Austrians, Austrian-British people, British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy o ...
also provided an important argument for extensionalism when he said that "a proposition is a truth-function of elementary propositions".

See also

Extension (semantics) In any of several fields of study that treat the use of signs — for example, in linguistics, logic, mathematics, semantics, semiotics, and philosophy of language — the extension of a concept, idea, or sign consists of the things to which it app ...
* Extension (predicate logic)


{{Reflist *Carnap, Rudolf: ''Der logische Aufbau der Welt''. Berlin-Schlachtensee 1928. Neuauflage Hamburg 1998. *Carnap, Rudolf: ''Logische Syntax der Sprache.'' Vienna 1934. *Carnap, Rudolf: ''Bedeutung und Notwendigkeit. Eine Studie zur Semantik und modalen Logik''. Wien/New York 1972 (Originalausgabe: ''Meaning and Necessity. A Study in Semantics and Modal Logic''. Chicago/Toronto/London 1947). *Quine, Willard Van Orman: "Three Grades of Modal Involvement", in: ''Proceedings of the 11th International Congress of Philosophy'', Vol. 14. Amsterdam 1953, 65–81. *Quine, Willard Van Orman: "Reference and Modality", in: ''From a Logical Point of View''. Cambridge (Massachusetts) 1953. *Quine, Willard Van Orman: ''Word and Object''. Cambridge (Massachusetts) 1960. *Quine, Willard Van Orman: ''Confessions of a Confirmed Extensionalist''. Cambridge (Massachusetts) 2008. Philosophy of language Logic philo-stub