incommensurability = not comparable by use of a common standard or measure
Kuhn-1962-structure-of-scientific-revolutions used the term incommensurability to characterize the holistic nature of change that takes place in a scientific-revolution. The normal-science that emerges from a scientific-revolution is not only incompatibility-of-successive-paradigms but often incommensurable.
Two rival paradigms can be compared well enough for it to be clear that they are incompatible. However, it is important to note that from within a paradigm, it is easy for scientists to claim why their paradigm is superior to others but from a neutral perspective, two people who work within different paradigms who are arguing about which is better will often appear to be talking past each other.
Two aspects of the problem of incommensurability
- people in different paradigms will not be able to fully communicate with each other, they will use key terms in different ways and in a sense be talking in slightly different languages
- even when communication is possible, people in different paradigms will use different standards of evidence and argument. They will not agree on what a good theory is supposed to do.
incommensurability of meaning
The view that people in different paradigms will not be able to fully communicate with each other because they will use key terms in different ways. This claim is based on the holistic view about the meaning of scientific language.
holistic view about the meaning of scientific language = This approach argues that theoretical terms cannot be understood in isolation; instead, they are meaningful only within the context of a “scientific web of belief
In other words, incommensurability of meaning is the idea that meaning of words derive from the paradigm in which they were used. When a paradigm changes (e.g. Newtonian to Einsteinian mechanics), key terms like “mass” or “space” change their meaning as well, becoming incomparable.
Example: Darwin and the concept “species”
- Before = species where like chemical elements, defined by the particular combinations of as-yet-unknown internal elements that make each individual the kind of thing it is
- After = species are like nationalities, loose clusters defined by the shared history and resembling one another mainly because of continuous interbreeding
incommensurability of standards
paradigm define what is a legitimate scientific question and what is an acceptable solution to that question, and so tend to bring their own standards of what counts as a good argument or good evidence.
Example: Aristotelian vs. Newtonian physics
In Aristotelian physics, explaining why a stone falls is straightforward: falling is part of the stone’s inherent nature. This teleological explanation was considered a successful account. But 17th-century mechanical philosophy revolutionized standards: a proper explanation must reduce all phenomena (color, taste, weight, motion) to the “size, shape, position, and motion” of matter particles—no appeals to inherent natures or purposes allowed. Under these new standards, “why does the stone fall?” becomes a genuine problem that the Aristotelian answer can no longer solve
When Newton introduced gravity as the innate attraction between particles, this was also seen as “occult” by 17th century physics standards, but the standards shifted again that mathematical predictive power now mattered more than mechanical explanation. What counts as a satisfactory explanation is thus incommensurable across these paradigms.