Tractarian Functions are not Propositional Functions

The central claim is that in the Tractatus Wittgenstein refuses Russell's notion of propositional function, and Russell's notions of range of significance and types for variables. Drawing on Russell's notion of well-defined function, for which all values are given in advance, Wittgenstein takes a different approach, that propositions realise a common characteristic, the general form, this being definitional of the propositional. This common characteristic is a formal concept, an Urbild (prototype), demonstrable by definition by abstraction. What is novel is the delimitation of the notion of a function fx in 5.501, and the argument showing that the general form, which Wittgenstein regards as a variable, is immanent to its realisations.