Extensional context

In philosophy of language, an extensional context' (or transparent context) is a syntactic environment in which a sub-sentential expression e can be replaced by an expression with the same extension and without affecting the truth-value of the sentence as a whole. Extensional contexts are contrasted with opaque contexts where truth-preserving substitutions are not possible.

Take the case of Clark Kent, who is secretly Superman. Suppose that Lois Lane fell out of a window and Superman caught her. Thus the statement, "Clark Kent caught Lois Lane," is true because it has an extensional context. The names "Superman" and "Clark Kent" have the same extension, which is to say that they both refer to the same person, i.e., that superhero who is vulnerable to kryptonite. Anybody that Superman caught, Clark Kent caught.

In opposition to extensional contexts are intensional contexts, where synonymous terms cannot be substituted in without potentially compromising the truth-value. Suppose that Lois Lane believes that Clark Kent will investigate a news story with her. The statement, "Lois Lane believes that Superman will investigate a news story with her," is false, even though Superman is Clark Kent. This is because 'believes' typically induces an intensional context.

See also

• Extension (semantics)
• Extensional definition
• Extensionalism
• Intensional logic
• Opaque context
• W.V. Quine

Further reading

• Francis Watanabe Dauer, Critical Thinking: An Introduction to Reasoning, Oxford University Press, 1989, p. 392.