Common cause explanation and the search for a smoking gun
The hypotheses of historical natural science are typically concerned with long past, singular events and processes, e.g., what caused the end-Cretaceous mass extinction. Evidence for such occurrences is acquired through field studies in the messy, uncontrollable world of nature. Because hypotheses about the remote past cannot be directly tested in the classical manner of experimental science, historical science is sometimes judged inferior. Building on earlier work, this essay explains the motivation for such arguments and why they are fundamentally mistaken. Traditional versions of the scientific method (inductivism and falsificationism) are based upon a deeply flawed, one-size-fits-all, logical analysis of the evaluative relation between hypothesis and observation. The distinctive methodologies of historical and experimental science, however, reflect pervasive causal differences in their evidential situations. The evidential reasoning of historical scientists is founded upon the principle of the common cause, which asserts that seemingly improbable associations among present-day traces of the past are best explained in terms of a common cause. The truth of the principle of the common cause rests upon a physically pervasive, time asymmetry of causation: In a nutshell, the present contains records of the past but not of the future. Viewed in this light historical scientists actually have an evidential advantage over classical experimentalists.