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.
[1] 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 (in his earlier work) and Willard Van Orman Quine were prominent proponents of this view.
[2] 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.
[2] The idea put forward by Richard Montague that the intension of a predicate or a sentence is identifiable from possible worlds to extensions is also attributed to Carnap.