Realism, rhetoric, and reliability

Abstract

Ockham’s razor is the characteristic scientific penchant for simpler, more testable, and more unified theories. Glymour’s early work on confirmation theory (1980) eloquently stressed the rhetorical plausibility of Ockham’s razor in scientific arguments. His subsequent, seminal research on causal discovery (Spirtes et al. 2000) still concerns methods with a strong bias toward simpler causal models, and it also comes with a story about reliability—the methods are guaranteed to converge to true causal structure in the limit. However, there is a familiar gap between convergent reliability and scientific rhetoric: convergence in the long run is compatible with any conclusion in the short run. For that reason, Carnap (1945) suggested that the proper sense of reliability for scientific inference should lie somewhere between short-run reliability and mere convergence in the limit. One natural such concept is straightest possible convergence to the truth, where straightness is explicated in terms of minimizing reversals of opinion (drawing a conclusion and then replacing it with a logically incompatible one) and cycles of opinion (returning to an opinion previously rejected) prior to convergence. We close the gap between scientific rhetoric and scientific reliability by showing (1) that Ockham’s razor is necessary for cycle-optimal convergence to the truth, and (2) that patiently waiting for information to resolve conflicts among simplest hypotheses is necessary for reversal-optimal convergence to the truth.