 Conceptual extension is important, especially since it served as one of the key initial motivations of Bridgman’s thought, but it is only part of the operationalist story. In more general terms, operationalism can be seen as a strategy for increasing the empirical content of scientific theories. What is empirical content? Karl Popper saw the amount of the empirical content of a theory as the number of states of the world that are forbidden by it. Regarding laws of nature he said: “the more they prohibit they more they say” (Popper 1972, 41). Or, somewhat more formally: “I define the empirical content of a statement p as the class of its potential falsifiers” (120). Similarly but staying away from the strict falsificationist idiom, Imre Lakatos understood empirical content as the number of empirically testable predictions. Empirical content is not something we hear about very much these days in philosophy of science after the receding of Popperian and Lakatosian doctrines, but for Bridgman and many other operationalists it was one of the key issues.