 The operationalist dictum could be phrased as follows: maintain and increase the empirical content of theories by the use of operationally well-defined concepts. It is difficult to craft an exact quantitative measure of empirical content, but we can at least say that the amount of empirical content depends on the number of empirically testable relations that a theory specifies. That, in turn, depends on the number of independently measurable parameters. Increasing the number of independent parameters, or at least maintaining it, was something that Bridgman sought to achieve with his operationalism. This, I submit, was one of the key reasons why he did not like conceptual extensions that were not backed up by measurement operations in the new domain. And it seems to me that this lesson was taken to heart by the operationist psychologists much more than the physicists, as Feest (2010; 2012) explains in her discussion of how operational definitions should be understood as tools of experimental investigation.