The No Relevant Alternatives Condition
The claim that delusions meet the No Relevant Alternatives Condition is supported by Daniel Freeman and colleagues' study on alternative explanations. Subjects with delusions were asked about the evidence for their delusional beliefs and the ‘availability of alternative explanations’ (Freeman et al. 2004: 677). Freeman and colleagues conclude from the study that:
‘we have found evidence that (at least at the height of the episode) individuals do not have accessible alternative explanations for their experiences. This seems to be caused by (a) a lack of awareness and knowledge about internal anomalous experiences, (b) reasoning biases, and (c) the difficulty of conceiving alternatives that are as compelling as the delusions in explaining personal experiences’
(Freeman et al. 2004: 679, my emphasis).
Coltheart and colleagues' (2009) work on abductive inference and delusional belief also supports the claim that delusions meet the No Relevant Alternatives Condition. Coltheart and colleagues argue that subjects with delusions form beliefs in line with a Bayesian model of abductive inference, according to which ‘one hypothesis H1 explains observations O better than another hypothesis H2 just in case P(O│H1) > P(O│H2)’ (Coltheart et al. 2009: 276).
Coltheart and colleagues think that the delusional hypothesis is more probable than the non-delusional hypothesis, given the observed phenomenon. Considering a case of the Capgras delusion, the two hypotheses in play are the stranger hypothesis (the woman who looks like my wife is not my wife) and the wife hypothesis (the woman who looks like my wife is my wife):
‘the observed data are clearly much more likely under the stranger hypothesis than under the wife hypothesis. It would be highly improbable for the subject to have the low autonomic response if the person really was his wife, but very probable indeed if the person were a stranger’
(Coltheart et al. 2009: 277).
Coltheart and colleagues' work here suggests that non-delusional alternative hypotheses are unavailable to subjects insofar as they are explanatorily unavailable. The delusional hypothesis just does a much better job of explaining the observed data, if what we mean by doing a better job is cashed out in terms of Bayesian probabilities.
The Epistemic Benefit Condition
What kinds of epistemic benefits might delusions enjoy? One benefit might be the filling of an explanatory gap. The subject may have an anomalous experience which they cannot explain, this may create in the subject ‘puzzlement, anxiety, and a search for an explanation’ (Maher 2006: 181). Perhaps the delusional hypothesis which makes some sense of the experience is better than no hypothesis at all (given the No Relevant Alternatives condition, there is no alternative). Maher suggests that delusional hypotheses are best thought of as like scientific theories—both ‘serve the purpose of providing order and meaning for empirical data obtained by observation’ (Maher 1988: 20). If this is right, the delusion is epistemically beneficial in providing an explanation of an as yet unexplained phenomenon.
Delusions might also be epistemically beneficial insofar as they make other perceptual beliefs coherent. A subject’s belief that she sees a second head on her shoulder, or that the person in the mirror does not look like her, might be made sense of by a delusional belief.
Delusions may also have indirect epistemic benefits. Maher suggests that for subjects with delusions, coherent explanations of their experiences are often accompanied by a ‘strong feeling of personal relief’, as well as the excitement a scientist might get from intellectual insight (Maher 1974: 104). The explanation for the anomalous experience that the delusional subject comes to may provide ‘enough relief from anxiety that it becomes difficult for the individual to abandon it and return to the initial state of confusion and distress’ (Maher 2006: 182). This relief from anxiety may have indirect epistemic benefits if the anxiety felt before coming to the delusional explanation for the anomalous experience was such as to adversely affect wellbeing and compromise the gaining of knowledge.