Lydia McGrew

I propose a measure of dependence that relates a set of items of evidence to an hypothesis H and to H's negation. I dub this measure relative consilience and propose a method for using it as a correction factor for dependence among items of evidence. Using RC, I examine collusion and testimonial independence, the value of diverse evidence, and the strengthening of otherwise weak or non-existent cases. RC provides a valuable tool for formal epistemologists interested in analyzing cumulative case arguments.

Both advocates and opponents of the fine-tuning argument treat multiple universes with a selection effect as a legitimate hypothesis to explain the life-permitting values of the constants in our universe. I argue that, except where there is specific relevant prior information, the occurrence of multiple instances of a low-likelihood causal process should not be treated as an alternative hypothesis to a higher-likelihood causal process. Since an ’ad hoc’ hypothesis can be invented to give high likelihood to any evidence, we must provide some epistemic rationale other than similar likelihood for comparing two hypotheses

It is often assumed by friends and foes alike of intelligent design that a likelihood approach to design inferences will require evidenceregarding the specific motives and abilities of any hypothetical designer. Elliott Sober, like Venn before him, indicates that this information is unavailable when the designer is not human (or at least finite) and concludes that there is no good argument for design in biology. I argue that a knowledge of motives and abilities is not always necessary for obtaining a likelihood on design. In many cases, including the case of irreducibly complex objects, frequencies from known agents can supply the likelihood. I argue against the claim that data gathered from humans is inapplicable to non-human agents. Finally, I point out that a broadly Bayesian approach to design inferences, such as that advocated by Sober, is actually advantageous to design advocates in that it frees them from the Popperian requirement that they construct an overarching science which makes high-likelihood predictions.

A focus on the conjunction of the contents of witness reports and on the coherence of their contents has had negative effects on the epistemic clarity of the Bayesian coherence literature. Whether or not increased coherence of witness reports is correlated with higher confirmation for some H depends upon the hypothesis in question and upon factors concerning the confirmation and independence of the reports, not directly on the positive relevance of the contents to each other. I suggest that Bayesians should shift focus to “coherence for” an hypothesis – that is, to the definition and analysis of cumulative case arguments in which a body of evidence supports some hypothesis that is not restricted to the conjunction of the contents of reports. Such a shift of focus will be valuable for approaching issues such as the problem of the external world which have interested Bayesian coherentists all along.

I offer an account of ad hocness that explains why the adoption of an ad hoc auxiliary is accompanied by the disconfirmation of a hypothesis H. H must be conjoined with an auxiliary a′, which is improbable antecedently given H, while ~H does not have this disability. This account renders it unnecessary to require, for identifying ad hocness, that either a′ or H have a posterior probability less than or equal to 0.5; there are also other reasons for abandoning that condition. I distinguish between formal ad hocness, which is bad in the probabilistic sense that it results in disconfirmation of H, and argumentative ad hocness, which actually involves bad reasoning on the part of a subject. The latter is what I call “not counting the cost.” This distinction allows us to see why the 0.5 condition appeared attractive in the first place. The concept of not counting the cost also has implications for other areas of research, including both a Bayesian concept of unfalsifiability and the classic epistemological question of the problem of the external world

Two different types of objections to the historical investigation of miracles imply that such investigation is inappropriate or can never lead to rational belief that a historical miracle has occurred. The first objection concerns the alleged chasm between the rational realm of history and the realm of faith. The second objection alleges that God is, or would be if he existed, too much unlike ourselves for us reasonably to use Divine action as an explanatory hypothesis. Both objections involve a tacit question-begging move against the traditional theistic hypothesis that a God exists who is capable of revealing himself to man by public signs. The theist should be free to test the hypothesis of a God who speaks rather than a God who is necessarily separated from his creatures.

In the debate over testimony to miracles, a common Humean move is to emphasize the prior improbability of miracles as the most important epistemic factor. Robert Fogelin uses the example of Henry, who tells multiple tall tales about meeting celebrities, to argue that low prior probabilities alone can render testimony unbelievable, with obvious implications for testimony to miracles. A detailed Bayesian analysis of Henry’s stories shows instead that the fact that Henry tells multiple stories about events that occurred independently if they occurred at all is crucial to his loss of credibility. The epistemic structure is similar to that of a case of multiple lottery wins by the same person. Each of Henry’s stories can confirm only one event, but all the stories confirm the hypothesis that Henry is a liar. This structure does not apply to testimony to just one event, however antecedently improbable. Such examples therefore do nothing to undermine a standard Bayesian analysis involving both priors and likelihoods in evaluating testimony to an improbable event.