Abstract

The determination of the meaning of theoretical terms by the axioms of theories as meaning postulates and the merely fictitious character of a basic observational language leads to Feyerabends problem of the incommensurability of physical theories. Different theories are actually compared by physicists as well. They might have a common sublanguage as the language of macroscopic physics in atomic physics. Furthermore shared metalaws (e. g. invariance principles) define an equivalence relation which identifies terms of different theories and enables physicists to talk about them in a common language.