Conspiracy Theories and the Hidden Evidence Penalty

Many regard conspiracy theories as intrinsically epistemically suspicious. Generalists defend this view, holding that there is something epistemically wrong with conspiracy theories as a class. Particularists deny it, contending that conspiracy theories must be evaluated on a case-by-case basis. This paper invokes a norm of theory choice from the philosophy of science and metaphysics to defend a weak form of generalism. According to the norm, we should prima facie disbelieve theories that posit undetectable entities. I develop a graded notion of undetectability, such that the more undetectable the posited structure, the greater the epistemic penalty a theory incurs. Conspiracy theorists, then, face a dilemma: either (1) posit a highly detectable (but undetected) conspiracy that should be rejected on evidential grounds or (2) posit a highly undetectable conspiracy that should be rejected on anti-undetectability grounds. Most conspiracy theories posit a high degree of secrecy, running into the second horn. This is illustrated through a range of examples, from “lizard people” to 9/11 “truthers.”