 A recent debate relevant to the rationality of delusions concerns the step from unusual events to delusional beliefs. (This is primarily an issue that emerged among two-factor theorists, so the language used below is acceptable to them, but the problem can be reformulated in terms that are friendly to prediction-error theorists.) Coltheart et al. 2010 argue that the step from unusual data to belief is an instance of abductive inference, as those who end up endorsing a delusional belief need to select an explanatory hypothesis for their unusual data from a range of relevant hypotheses. Coltheart and colleagues use the Bayesian model of abductive inference which invites us to ask two questions: Which hypothesis better explains the data? Which hypothesis is the most plausible given what we already know? In the case of delusions, they argue, it is reasonable to adopt the delusional hypothesis given the data, and the good fit between hypothesis and data swamps general considerations about the overall implausibility of the hypothesis. What may not be reasonable is the fact that people with delusions hang onto their delusions even when they keep gathering evidence against it, that is, the delusional belief is not correctly updated in the light of new information. The authors argue that the information undermining the delusional hypothesis does not present itself as disconfirming evidence to the person with the delusion. Thus, the new evidence is interpreted in the light of the delusion and confabulation is used to fill the gaps. The behaviour of the person with the delusion is not very different from that of an obstinate scientist refusing to see that the new data undermines the support for the theory she is deeply committed to.