Incommensurability

When one scientific theory or tradition is replaced by another in a scientific revolution, the concepts involved often change in fundamental ways. For example, among other differences, in Newtonian mechanics an object’s mass is independent of its velocity, while in relativity mechanics, mass increases as the velocity approaches that of light. Earlier philosophers of science maintained that Einsteinian mechanics reduces to Newtonian mechanics in the limit of high velocities. However, Thomas Kuhn (1962) and Paul Feyerabend (1962, 1965) introduced a rival view. Kuhn argued that different scientific traditions are defined by their adherence to different paradigms, fundamental perspectives which shape or determine not only substantive beliefs about the world, but also methods, problems, standards of solution or explanation, and even what counts as an observation or fact. Scientific revolutions (changes of paradigm) alter all these profoundly, leading to perspectives so different that the meanings of words looking and sounding the same become utterly distinct in the pre- and post-revolutionary traditions. Thus, according to both Kuhn and Feyerabend, the concepts of mass employed in the Newtonian and Einsteinian traditions are incommensurable with one another, too radically different to be compared at all. The thesis that terms in different scientific traditions and communities are radically distinct, and the modifications that have stemmed from that thesis, became known as the thesis of incommensurability.