What does extensionality show in the Tractatus?

  • Sascha Rammler


Extensionality and extensionalism are common themes in Analytic Philosophy. The early Wittgenstein of the Tractatus is also taken to hold a thesis of extensionality. Extensionality in the Tractatus is associated with sentence 5, where Wittgenstein claims that a proposition is a truth-function of elementary propositions. The notion of a truth-function in the Tractatus is approached by an operational view in this paper that takes the truth-functions themselves as generated by a truth-operation. In this sense, the truth-operation is generating the notation itself, not an interpretation of some formal language. Extensionality in the Tractatus is approached in three steps, illustrating first what an operational reconstruction can show about extensionality, continuing with the role the Tractatus assigns to extensionality, and concluding by comparing it to other uses of the term extensionality in the Analytic tradition.

Keywords: Extensionality; Truth functionality; Early Wittgenstein; Tractatus.