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.
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 sentence " Superman caught Lois Lane " is true . Because this sentence is an extensional context , the sentence " Clark Kent caught Lois Lane " is also true. Anybody that Superman caught, Clark Kent caught. In opposition to extensional contexts are intensional contexts, where terms cannot be substituted without potentially compromising the truth-value. Suppose that Lois Lane believes that Clark Kent will investigate a news story with her. Thus, the sentence "Lois Lane believes that Clark Kent will investigate a news story with her" is true. However, the statement, "Lois Lane believes that Superman will investigate a news story with her," is false . This is because 'believes' typically induces an intensional context. Lois Lane doesn't believe that Superman is Clark Kent and the propositional attitude "believe" induces an intensional context, so the substitution alters the meaning of the original sentence. See also De dicto and de re Extension (semantics) Extensional definition Extensionalism Intensional logic Opaque context Propositional attitude W.V. Quine Further reading Francis Watanabe Dauer, Critical Thinking: An Introduction to Reasoning , Oxford University Press, 1989, p. 392.
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