Second Guessing: A Self-Help Manual

Abstract

I develop a general framework with a rationality constraint that shows how coherently to represent and deal with second-order information about one's own judgmental reliability. It is a rejection of and generalization away from the typical Bayesian requirements of unconditional judgmental self-respect and perfect knowledge of one's own beliefs, and is defended by appeal to the Principal Principle. This yields consequences about maintaining unity of the self, about symmetries and asymmetries between the first- and third-person, and a principled way of knowing when to stop second-guessing oneself. Peer disagreement is treated as a special case where one doubts oneself because of news that an intellectual equal disagrees. This framework, and variants of it, imply that the typically stated belief that an equally reliably peer disagrees is incoherent, and thus that pure rationality constraints without further substantive information cannot give an answer as to what to do. The framework also shows that treating both ourselves and others as thermometers in the disagreement situation does not imply the Equal Weight view.

Respecting all the evidence

“…Whether such general defeaters are possible is controversial. (See Roush [2009] for skepticism about this.). Supposing that such situations can come about, one possible response is to say that, in such cases, the rational requirements are undefined.…”

Knowledge of Our Own Beliefs

“…(Cf. Roush , 253.) A subject following this principle is safe against sure loss since SR is safe and this is SR over a restricted domain.…”

“…On the other hand, when there are probability statements besides P(H) = x that a subject has beliefs about, NGI does not apply, and nothing says that conditioning on a statement of your degree of belief in that kind of case could not change your degree of belief. The awkward situation described above is a class of cases in which the further assumptions 1–4 make the statement of what the subject's degree of belief is relevant to the probability of H. Principles for handling such cases have values other than x on the right‐hand side, and so can underwrite changes in first‐order degrees of belief on the basis of beliefs about one's beliefs by conditionalization, and this is so even if one has an extreme degree of belief about P(H) = x (Roush ). Thus NGI does not force second‐order probabilities to be inert.…”

“… The counterexamples to SR given in Skyrms (), Christensen (, ), Roush (), and Lasonen‐Aarnio () all appeal to suppositions relevant to the relation of the subject's beliefs to the world—optimism, drug consumption, empirical psychological evidence of unreliability, angel communications. They can be represented in the form of conditions 1–4 because those suppositions must be matters the subject has degrees of belief in if she is to be expected to take them into account.…”

The Rationality of Science in Relation to its History

“…What is relevant here is that the rule I have defined (Roush 2009) demands a proportionality that explains why if we have evidence that the history of scientific failures is sufficiently relevant to our general reliability about things like the existence of muons and quarks, then our scientist does have a problem with particular claims about muons and quarks. This is because if a high fraction of our predecessor's theories about q-matters have been wrong, say 80%, then the fraction of q-matters we are likely wrong about is 80%, and only 20% are still to be considered right.…”