The mirror metaphor and the notion of an extension function
The aim of this article is to analyze the notion of the extensional propositional function (introduced by Frank P. Ramsey) in the context of logicism program in a field of foundations of mathematics and in the context of opposition between intentionalism and extensionalism. In what follows the article consider Wittgenstein's arguments against the use of function-in-extension as a replacement in place of identity sign. In elucidating the mirror metaphor (used by Wittgenstein in his controversy with Ramsey) I try to make specialized some crucial points of Wittgenstein's disagreement with logicism as a kind of philosophical approach to mathematics.