It has recently been suggested that delusions be conceived of as symptoms on the harmful dysfunction account of disorder: delusions sometimes arise from dysfunction, but can also arise through normal cognition. Much attention has thus been payed to the question of how we can determine whether a delusion arises from dysfunction as opposed to normal cognition. In this paper, we consider another question, one that remains under-explored: which delusions warrant treatment? On the harmful dysfunction account, this question dissociates from the (...) question about dysfunction—there are a broad range of “treatable conditions” beyond mere harmful dysfunctions. As such, many conditions that arise from normal cognition are also eligible for medical intervention. We argue that some delusions that arise from normal cognition may well fall under the banner of treatable conditions. We examine the practical and ethical questions surrounding such treatment, including the issue of coercive and deceptive treatment options. (shrink)

The dominant conception of delusion in psychiatry (in textbooks, research papers, diagnostic manuals, etc.) is predominantly epistemic. Delusions are almost always characterized in terms of their epistemic defects, i.e., defects with respect to evidence, reasoning, judgment, etc. However, there is an individualistic bias in the epistemic conception; the alleged epistemic defects and abnormalities in delusions relate to individualistic epistemic processes rather than social epistemic processes. We endorse the social epistemological turn in recent philosophical epistemology, and claim that a corresponding turn (...) is needed in the study of delusions. It is a turn from the (purely) individualistic conception, which characterizes delusions only by individualistic epistemic defects and abnormalities, to the (partially) social epistemic conception, which characterizes delusions by individualistic as well as social epistemic defects and abnormalities. This paper is intended as an initial step toward such a social epistemological turn. In particular, we will develop a new model of the development of delusions according to which testimonial abnormalities, including testimonial isolation and testimonial discount, are a causal factor in the development of delusions. (shrink)

The Capgras delusion is a condition in which a person believes that an imposter has replaced some close friend or relative. Recent theorists have appealed to Bayesianism to help explain both why a subject with the Capgras delusion adopts this delusional belief and why it persists despite counter-evidence. The Bayesian approach is useful for addressing these questions; however, the main proposal of this essay is that Capgras subjects also have a delusional conception of epistemic possibility, more specifically, they think more (...) things are possible, given what is known, than non-delusional subjects do. I argue that this is a central way in which their thinking departs from ordinary cognition and that it cannot be characterized in Bayesian terms. Thus, in order to fully understand the cognitive processing involved in the Capgras delusion, we must move beyond Bayesianism. 1 The Simple Bayesian Model2 Anomalous Evidence and the Capgras Delusion3 Impaired Reasoning4 Setting Priors5 Epistemic Modality6 Delusions of Possibility7 Delusions of Possibility in Different Contexts8 How Many Factors? (shrink)

Folie à deux is the transference of delusional ideas from one 'primary' individual to one or more 'secondary' individuals (Lasègue & Falret, 1877). However, it is difficult to investigate experimentally because often only one patient is identified as delusional. We investigated whether hypnosis could model the experiences of the secondary in this delusion. Our primary was a confederate, who displayed two delusional beliefs and attempted to transmit them to hypnotised subjects. We manipulated the status of the confederate so that they (...) were portrayed as either "credible" or merely "interesting". Many high hypnotisable individuals adopted the confederate's beliefs and confabulated evidence in support of them. Also, subjects who interacted with a credible confederate extended their delusions beyond those displayed by the confederate. We discuss the strengths and limitations of this approach and suggest ways to improve the validity of this model. (shrink)