Just as there is no unitary "scientific method," faithful following of which guarantees scientific advances, there is not likely to be a productive, rule-like economic methodology. For example, Friedman noted that the "rules for using [a] model ... cannot possibly be abstract and complete." How the "entities in [a] model" are to be connected to "observable phenomena ... can be learned only by experience and exposure in the right' scientific atmosphere, not by rote" (1953a, p. 25). And on page 9 of the 1953 essay he inserted a crucial parenthetical phrase into the passage putting forward falsificationism, writing that a hypothesis should be "rejected if its predictions are contradicted (frequently' or more often than predictions from an alternative hypothesis)" a formulation that left room for the exercise of professional judgment.

Donald MacKenzie, An Engine, Not a Camera, loc. 59