Stanford Encyclopedia Entry on Delusions.

In her book “Are Mental Disorders Brain Disorders?” (2022), Anneli Jefferson proposes that brain processes that always realize mental dysfunctions are brain dysfunctions. This paper explores possible interpretations of two underdeveloped aspects of this thesis. First, it argues that “realization” should be interpreted as partial rather than full realization. Second, it argues that the “always” should only quantify over biologically normal situations. Taken together, these changes can account for the fact that some psychological dysfunctions are partially realized by functional mechanisms, (...) for the existence of psychological dysfunctions due to mismatches rather than brain dysfunctions, and for the fact that brain dysfunctions do not cease to be brain dysfunctions just because they can be compensated. (shrink)

In his recent book Delusions and Beliefs, Kengo Miyazono offers a thoroughgoing defence of delusions as biologically malfunctioning beliefs, greatly elaborating on his earlier defence of this view. Miyazono has it that delusions have biological doxastic functions, and that delusions involve direct or indirect malfunctions of this kind. In this short piece, I focus on Miyazono’s defence of a two-factor approach to delusion formation as it appears in Chapter Four. Miyazono approaches his discussion of the debate between one- and two-factor (...) theories having already defended the key thesis of the book: that delusions are malfunctioning beliefs. Of course, that thesis might be thought to mesh nicely with the two-factor theorist’s claim that there is a cognitive abnormality present in delusion formation or maintenance. However, I will discuss Miyazono’s defence of the two-factor position in isolation from its role in his overall account of delusion. Miyazono abstracts away from the particulars of Max Coltheart’s two-factor view, and takes himself to be investigating the plausibility of two-factor theories without the specific commitments of Coltheart’s view. Miyazono also captures under the two-factor heading theories which locate the second factor in belief maintenance rather than just in belief formation. He puts forward a new argument for a two-factor approach which goes via inference to the best explanation. I begin by arguing that Miyazono’s starting motivation for a two-factor approach rests on a misrepresentation of the one-factor approach. Then, I turn to the four components of Miyazono’s inference to the best explanation argument, and argue that in each case, we do not have grounds for positing a second factor. (shrink)

Kengo Miyazono’s Delusions and Beliefs: A Philosophical Inquiry is an attempt to provide a unified account of the nature, pathology, and etiology of delusions. The strength of his book resides in the clarity of arguments and its consistent adoption of a biological explanation of delusions, based on teleo-functionalism about mental states. However, there are some weaknesses in each of his arguments regarding the nature, pathology, and etiology of delusions. Regarding the nature of delusions, teleo-functionalism makes it difficult to confirm that (...) delusions are beliefs. Regarding the pathology of delusions, I suggest that the existence of harmful malfunction is a necessary but not a sufficient condition for a belief to be considered pathological, and that additional evidence is needed to justify the separation of the belief and the holder’s personhood. Regarding the etiology, it is not reasonable to incorporate the prediction error theory into a kind of two-factor theory. Therefore, the details of his arguments require further modification. (shrink)

The central hypothesis of this book, Delusions and Beliefs: A Philosophical Inquiry (Routledge, 2019), is that delusions are malfunctional beliefs (Chapter 1); they belong to the category of belief (Chapter 2) but, unlike mundane false or irrational beliefs, they fail to perform some functions of belief (Chapter 3). More precisely, delusions directly or indirectly involve some malfunctioning cognitive mechanisms, which is empirically supported by the two-factor account of delusion formation (Chapter 4).

Kengo Miyazono, in his work Delusions and Beliefs, defends a teleo-functional account of delusions. In my contribution to this symposium, I question one of Miyazono’s motivations for appealing to teleo-functionalism over its main rival, dry-functionalism. Miyazono suggests that teleo-functionalism, unlike dry-functionalism, can account for the compatibility of the theses (i) that delusions are genuine doxastic states (doxasticism about delusions) and (ii) that delusions do not perform the typical causal roles of beliefs (the causal difference thesis). I argue, however, that there (...) are also ways for dry-functionalism to account for this compatibility. If what I have to say is correct, then Miyazono is perhaps too hasty—at least in one important respect—to opt for teleo-functionalism over dry-functionalism. Dry-functionalism has an equally good chance of satisfying some of Miyazono’s explanatory goals. (shrink)

The standard position in psychiatry maintains that delusions are beliefs. However, the features of delusions often diverge from those typically associated with belief. This discrepancy has given rise to what I refer to as the doxastic status debate, which concerns whether delusions are best characterized as “beliefs.” Despite efforts, there has been little progress in settling this debate. I argue that the debate has been stymied because it’s largely a verbal dispute (Chalmers, 2011). I then attempt to advance the debate (...) into substantive territory by putting forward the hetero-dynamic property cluster (HDPC) model. According to the HDPC model, delusions are mental states characterized by an odd and unstable cluster of features, which, when manifested, gives delusions the appearance of straddling the line between two distinct types of attitudes. (shrink)