Kuhn 3: Incommensurability

"Incommensurability" is a metaphor. For the most part, what Kuhn calls "incommensurable" are words (though of course, when words don't match, the numbers you'd get from actually "measuring" what the words are supposed to designate would be suspect). Kuhn's metaphor compares words to geometry: The hypotenuse of an isosceles right triangle is incommensurable with its side in that there's no way you can measure one against another and get an integer. There's always some remainder. So, by analogy, certain crucial terms from Aristotle's physics are incommensurable with Newton's physics in that you can't find terms in the latter that can match up with those crucial terms from the former without there being a leftover, a remainder, a residue.

( bodies in motion )