Friedman's methodological views were, therefore, not a precise prescription for how economics should be done. His view that economic theory was "an `engine' to analyze [the world], not a photographic reproduction of it" (1953a, p. 35) was in a sense a truism: a theory that incorporates all detail, as if photographically, is clearly as much an impossibility as a map that reproduces exactly every aspect and feature of terrain and landscape. Nevertheless, the view that economic theory was an "engine" of inquiry, not an (infeasible) camera faithfully reproducing all empirical facts, was important to the developments discussed in this book.

Donald MacKenzie, An Engine, Not a Camera, loc. 61