 Kuhn modeled the history of a science as a succession of dogmatic periods of “normal science” under a “paradigm”, separated by “revolutionary” transitions to the next paradigm. According to Kuhn such a break from the past rejuvenates a field that had stagnated under the weight of anomalies that it no longer seemed to have the resources to solve. A new paradigm introduces changes at all levels, from established databases and instrumentation to the conceptual framework, goals, standards, institutional organization, and research culture—so much so that some older practitioners can hardly recognize the new paradigm as their field. This disconnect produces “incommensurability” across paradigm change, ranging from communication failure to problems of rational choice between the two, since there exists no fixed measure of success. At his most radical, Kuhn modeled revolutionary decisions on political revolution at the community level and on religious conversion at the individual level, adding that scientists on different sides of a paradigm debate “live in different worlds” ([1962] 1970a: ch. 10). Under critical pressure, he subsequently softened his position. In fact, he sought to clarify the notion of incommensurability to the end of his life (Sankey 1997). Kuhn exemplifies the irony that, while historicists used deep change as a weapon to beat up traditionalists, it presented serious problems for the historicists themselves as well.