 What was Kuhn’s revised conception of rationality and how was it based on history (to the degree that it was)? While he provided no explicit, general theory of rationality, Kuhn’s challenge here was greater than many appreciate. The positivists and Popperians had practically invented modern, academic philosophy of science. For them, scientific rationality was wholly a matter of making correct theory acceptance decisions in context of justification, where the hypotheses and test data are already on the table, the data are theory-neutral, and the goals and standards are logically independent of theory. To Kuhn this picture of science was more like a photographic negative in which light and dark are reversed. Let us count the ways.