So far, we have examined how Kuhn modified his understanding of scientific revolutions and paradigms and their roles in scientific inquiry and scientific change. Scientific revolutions and paradigms are two of the central concepts in Structure. A third key concept introduced in Structure concerned Kuhn throughout his career, namely incommensurability. Rather than trace the history of the use of this term, as we did with the concept of “paradigm,” my aim here is to distinguish the variety of ways in which Kuhn used the term “incommensurability.”

Kuhn regarded the notion of incommensurability as extremely important to understanding scientific change. In fact, in 1990, he claimed that his “own encounter with incommensurability was the first step on the road to Structure,” adding that “the notion still seems … the central innovation introduced in the book” (1993/2000, 228). Later in his career, Kuhn devoted more and more energy to the issue of incommensurability.