Commensurability, Comparability, Communicability

Twenty years have passed since Paul Feyerabend and I first used in print a term we had borrowed from mathematics to describe the relaationship between successive scientific theories. ‘Incommensurability’ was the term; each of us was led to it by problems we had encountered in interpreting scientific texts (Feyerabend 1962; Kuhn 1962). My use of the term was broader than his; his claims for the phenomenon were more sweeping than mine; but our overlap at that time was substantial. Each of us was centrally concerned to show that the meanings of scientific terms and concepts — ‘force’ and ‘mass’, for example, or ‘element’ and ‘compound’ — often changed with the theory in which they were deployed. And each of us claimed that when such changes occurred, it was impossible to define all the terms of one theory in the vocabulary of the other.