Essays in Positive Economics

Friedman argues that economics should be a positive science—concerned with what is, not what ought to be—and that the ultimate goal is developing theories that yield valid predictions about phenomena not yet observed . He rejects judging theories by the realism of their assumptions, claiming that truly significant hypotheses have assumptions that are 'wildly inaccurate descriptive representations of reality' . The test of a theory is whether it predicts well, not whether its premises correspond to observed behavior. This position became known as methodological instrumentalism .

The essay introduced the 'as if' methodology: firms may be treated as if they are maximizing profits, even if surveys of businessmen reveal no such calculation . Friedman argued that if the hypothesis that firms act as if maximizing profits generates accurate predictions, the question of whether they consciously calculate marginal revenue and cost is irrelevant. This principle, combined with his claim that unrealistic assumptions do not invalidate a theory, provided a methodological defense for neoclassical models of perfect competition and profit maximization that critics attacked for descriptive inaccuracy .

Philosophers of economics have largely rejected Friedman's argument. Uskali Mäki argues that the essay contains no unambiguous doctrine—it offers an 'F-Mix' of ambiguous and inconsistent ingredients that cannot be reduced to a single coherent methodology . Critics note that the distinction between assumptions and implications is superficial, since assumptions are testable and apparent disconfirmations cannot be dismissed . Lawrence Boland defends Friedman, arguing that critics misread the essay and that its instrumentalist logic is sound . The debate over what Friedman 'really meant' remains unresolved .

The most common misreading treats Friedman's claim as a blanket endorsement of any unrealistic assumption whatsoever. In fact, Friedman specifies that descriptive unrealism alone does not make a theory significant . The assumptions must extract only those elements crucial for prediction while omitting predictively irrelevant details. The choice of what to neglect is justified by whether it contributes to predictive success, not by arbitrary preference . Friedman's argument is about which unrealisms are acceptable, not whether all unrealisms are acceptable. This nuance is frequently lost in textbook summaries that reduce the essay to a slogan.

The essay provides the methodological justification for the Chicago school's characteristic approach: building simple, abstract models that generate testable predictions, with less concern for descriptive realism than for predictive accuracy . Melvin Reder noted that a significant minority of Chicago economists, including Coase and Buchanan, rejected Friedman's criterion in favor of intuitive appeal or axiomatic compatibility . Nevertheless, Friedman's argument shaped how generations of Chicago-trained economists defended their methods. The essay is described as 'the most influential work on economic methodology of this century' .

There is tension between Friedman's methodological prescriptions and his actual work. Kevin Hoover's research on Friedman and Schwartz's A Monetary History found that Friedman used causal language extensively, suggesting a realist stance inconsistent with pure instrumentalism . Friedman also rejected formalist economics in practice, emphasizing Marshallian tools over Walrasian general equilibrium . Some scholars argue that Friedman's methodology and 'the methodology of F53' are not identical—the essay may not fully capture how Friedman himself conducted research .