incommensurability = not comparable by use of a common standard or measure
Incommensurability is a direct consequence of viewing scientific-revolutions-as-changes-of-world-view.
Kuhn-1962-structure-of-scientific-revolutions used the term incommensurability to characterize change that takes place in a scientific-revolution. After a scientific-revolution, there is not only incompatibility-of-successive-paradigms but also incommensurability. This means that we are unable to compare or measure two theories, paradigms, or concepts against each other due to lack of a common standard or shared framework.
Example:
- In Newtonian physics, mass is defined as while for Einstein, . In this sense, mass is no longer comparable between the two theories.
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. It becomes impossible to compare two paradigms when they are incommensurable and so how can we say that we are progressing towards the truth.
“Kuhn coined his aphorism that revolutions progress away from previous conceptions of the world that have run into cataclysmic difficulties. ” (Introductory Essay, Ian Hacking)
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.
Consequences of incommensurability
Not being able to compare two theories means that there is no rational ground for preferring one theory to another.
Kuhn described scientific-revolution as progressing away from previous conceptions of the world that have run into cataclysmic difficulties. This and the notion of incommensurability challenges the idea the science aims for truth. Kuhn rejects this notion and instead focuses on the values that science should focus on.
When it came to theory choice, Kuhn pointed out that it is more of a conversion rather than a choice. In school, you are never given the choice of which theory you are learning. You are indoctrinated into whatever theory is dominant at the time. The choice was made for you.