Delusional beliefs are typically pathological. Being pathological is not the same as being false or being irrational. A woman might falsely believe that Istanbul is the capital of Turkey but it might just be a simple mistake. A man might believe without good evidence that he is smarter than his colleagues, but it might just be a healthy self-deceptive belief. On the other hand, when a patient with brain damage caused by a car accident believes that his father was replaced by an imposter, or when another patient with schizophrenia believes that 'The Organization' painted the doors of the houses on a street to send a message to him, these beliefs are not merely false or irrational. They are pathological.
What makes delusional beliefs pathological? One might think, for example, that delusions are pathological because of their extreme irrationality. The problem with this view, however, is that it is not obvious that delusional beliefs are extremely irrational. In a recent debate about the two-factor theory, Max Coltheart, Peter Menzies, and John Sutton (2010) argue that it is rational from the Bayesian point of view at least, to adopt delusional hypotheses given their neuropsychological deficits.
McKay (2012), on the other hand, argues that adopting delusional hypotheses is due to the irrational bias of discounting the ratio of prior probabilities. Even if McKay is correct, however, it is not clear that adopting delusional hypotheses is irrational since the bias of discounting prior probabilities has been found among normal people as well (e.g., Kahneman & Tversky 1973). Also, it is worth pointing out that some psychological experiments seem to show that people with delusions are, in some respects, more rational than normal people (e.g., Huq et al. 1988).
In my paper, Delusions as Harmful Malfunctioning Beliefs, I also examine the views according to which delusional beliefs are pathological because of (1) their strange content, (2) their resistance to folk psychological explanations and (3) the impaired responsibility-grounding capacities. I provide some counterexamples and theoretical problems for these proposals.
I argue, following Wakefield’s (1992a, 1992b) harmful dysfunction analysis of disorder, that delusional beliefs are pathological because they involve some kinds of harmful malfunctions. In other words, they have a significant negative impact on wellbeing (harmful) and, in addition, some psychological mechanisms, directly or indirectly related to them, fail to perform the jobs for which they were selected in the evolutionary history (malfunctioning). (I have blogged about this in the past, see here.)
There can be two types of objections to the proposal. The first type of objection is that delusional beliefs might not involve any malfunctions. For example, they might be playing psychological defence functions properly. The second type of objection is that a harmful malfunction is not sufficient for a mental state to be pathological. For example, false beliefs might involve some malfunctions according to teleosemantics (Dretske 1991; Millikan 1989). But, a harmful false belief might not be pathological. I examine the objections in detail and conclude that the proposal can be defended from the challenges.