Are delusions pathological, adaptive, or both? I investigated this issue with Lisa Bortolotti. We framed the question in the context of one of the most popular theories of delusion formation and maintenance: the two-factor theory.
Two-factor theories hold that the formation and maintenance of delusions involve two factors. Factor 1 is usually a neuropsychological impairment, while Factor 2 is a cognitive deficit or bias. While two-factor theorists agree on the broad two-factor architecture involved in the formation and maintenance of delusions, they disagree on some aspects of it. Coltheart and McKay are among the most prominent two factor theorists.
While for Coltheart, Menzies and Sutton (2010) Factor 2 is a cognitive deficit that only gets activated in the maintenance stage of delusions, for McKay (2012) it is a bias that is already present when delusions are adopted. In other words, for Coltheart delusions are initially a rational explanation of the anomalous feelings or experiences engendered by Factor 1, but they then become problematic when maintained in the face of counterevidence. For McKay instead, adopting the delusion in the first place is already problematic. Therefore, according to McKay, a bias in reasoning – though not a deficit - must already be present in the adoption stage of delusions.
How do these theories relate to the notion of pathology? We argue that in the Coltheart model, delusions are pathological both on a normativist and naturalist view. On a normativist view, delusions are pathological because they disrupt psychological functioning, while on a naturalist view, delusions are pathological because they are due to a cognitive dysfunction (Factor 2 in the Coltheart model). For McKay, delusions are not pathological on a naturalist view, because their formation and maintenance are due to a bias rather than to a dysfunction, while they can be pathological on a normativist view, because they can disrupt psychological functioning.
What about the relationship that such theories entertain with adaptiveness? Delusions are adaptive if they are designed to act as an emergency mechanism, providing psychological or biological benefits in the face of adversities, traumas or cognitive impairments. On Coltheart’s reading, maintaining delusions in the face of counterevidence could be a response to a crisis that prevents the cognitive system from collapsing, so delusions might be adaptive. On McKay’s model, adopting some delusions could be a response to a crisis that prevents the cognitive system from collapsing, so delusions could be adaptive when adopted. This is compatible with those delusions being the outcome of a cognitive bias.
The conclusion of our investigation is somewhat surprising. In the McKay model, some delusions can be pathological and adaptive, though not at the same time. Adaptive, because they prevent the person’s cognitive system from breaking down when adopted; pathological, on a normativist account, because they disrupt the person’s psychological functioning in the long-term. However, in the Coltheart model, delusions cannot be adaptive and pathological, because the fact that they are the outcome of a dysfunction (pathological in a naturalist sense) is incompatible with the possibility that they are the outcome of an emergency mechanism which breaks by design.