1 Introduction

Why Delusions Matter is a reflection on the importance of the study of delusions for better understanding and reshaping our mutual interactions. The study of delusions has transformed the philosophy of mind and psychology in the last thirty years, helping redefine the relationship between rationality and intentionality, and I think it has still a lot to give to emerging areas at the intersection of ethics and epistemology. These are areas where the focus of the investigation of people’s beliefs is moving from a painstaking assessment of the individual’s cognitive achievements and failures to a broader examination of social pressures on the adoption and maintenance of beliefs at the individual and collective level.

The book has two main aims: one is descriptive and the other is revisionist. In the descriptive part, it offers an analysis of how we attribute delusions—when it is that we characterise someone’s report as a delusion. We tend to attach the label “delusional” to those beliefs that are implausible to us and that serve the function of unshakeable identity beliefs for the speaker. One implication of attributions of delusionality is that the person reporting the belief is not in their right mind or has their agency compromised—the delusion would be a sign that something has gone wrong. In the revisionist part, the book proposes a reconceptualization of delusions, challenging the view that delusions are pathological beliefs, and that the presence of delusions is a mark of the speaker’s compromised agency. To contrast the common conception of delusions as pathological beliefs, the book features a detailed discussion of their harmful consequences and potential benefits, and also considers whether delusions are the output of malfunctioning belief formation and maintenance processes.

In part 1 of the book I argue that attributions of delusionality are driven by perceived features of the person’s report that are predominantly epistemic: the speaker seems to report an identity belief that is not given up in response to external challenges and appears implausible to the interpreter, where implausibility is defined in terms of being difficult to believe. In addition to these epistemic features, there is another important feature that is only in part epistemic: the belief may start out as something peripheral to the speaker’s concerns but soon becomes quite central to their conception of the world and of themselves.

In part 2 of the book I argue that we have no good reason to see delusions as pathological beliefs and that delusions can be associated with harm, but they are not always the origin of the harm that is experienced by the speaker or their close or wider social circle. I suggest that delusions are often a response to a puzzling reality—the origin of the harm may be already there, and all the delusion is doing is respond to it, often in a suboptimal and counterproductive way. One important consideration is that by relying on the delusion to explain a challenging reality, the speaker sees delusions as meaningful, and interpreters could do the same if informed about the speaker’s situation and experiences.

2 Judgements of delusionality

In chapter 1, “Delusions as investments”, I start with some examples of beliefs that are considered delusional, both in clinical and nonclinical context, and ask whether those examples have anything in common. In her memoir on living with schizophrenia, Elyn Saks writes that she thought houses were sending her messages about herself. In her defence of her stance about COVID, denialist Kelly Brogan claimed that there is no germ transmission. Both reports, “The houses are sending me messages” and “There is no germ transmission”, have been considered delusional. Why?

I answer that question within the framework of interpretation—the situation where, in a shared environment, a speaker makes a report and an external observer, an interpreter, attempts to assign meaning to that report. What features of the report lead the interpreter to attribute a delusion to a speaker? One first feature is that the report is something the speaker seems to report with conviction and sincerity: it is not meant as a joke, but it is something the speaker may follow up by defending the report from challenges or even acting on it. In this sense, attributions of delusionality happen when the report is something the speaker has some investment in.

In chapter 2, “Delusions and the world”, I tackle the perceived relationship between the report that is described as delusional and reality. It is common to assume that delusions are false, and even more than false, bizarre. Bizarreness is meant to capture the sense in which the content of the belief is not merely false, but it is logically or physically impossible. However, I offer some reasons to resist the idea that attributions of delusionality track judgements of bizarreness or falsity. The most common delusions in schizophrenia, jealousy and persecution, do not have an impossible content and can be true, yet they attract judgements of delusionality. I argue that the key notion is that of implausibility. For the interpreter, and sometimes for the speaker as well, the report is hard to believe. Often this is due to the fact that it clashes with other things that are commonly accepted as true. In the case of Elyn Sachs believing that houses are sending her messages, the belief conflicts with the knowledge that, outside of science fiction, inanimate objects do not communicate with us. In the case of Kelly Brogan disputing germ transmission, the belief clashes with one of the pillars of contemporary medicine.

In chapter 3, “Delusions and evidence”, I consider whether key elements of attributions of delusionality are that the report is groundless, or that is insensitive or irresponsive to evidence. I argue that although the relationship between the content of the report and the evidence for or against it is central to the notion of delusion, it would be a mistake to assume that people who report delusions do so without reason or are indifferent to external challenges. Often there is some experience backing up the speaker’s report, though the delusion may not be the best way to make sense of that experience. And the speaker does realise when challenges are made to the delusional report and often further articulates it to protect it from such challenges. This shows sensitivity to evidence, to an extent. However, what seems key to delusions, though not unique to them, is that evidence or arguments against them are unlikely to lead to a rejection of the belief. I call this unshakeability.

In chapter 4, “Delusions and identity”, I argue that attributions of delusionality are guided by the assumption that the subject of the report for the speaker is not something marginal, but something that comes to reflect and shape their sense of themselves in relation to their environment. When interpreters say: “That’s delusional!”, they assume that the report is an identity belief for the speaker, that is, something stable and action guiding that the speaker believes to be an expert about and cares about. I noticed earlier how the report attributed to the speaker as a delusion is not a good fit with the interpreter’s and sometimes even the speaker’s beliefs. That notwithstanding, the report that is characterised as delusional often expresses some of the speaker’s values. Even when it is about the external world as opposed to being about the speaker, as in the idea that there is no germ transmission, it embodies some of the speaker’s ways of understanding the world. The denial of germ transmission and the rejection of some medical interventions fit with a view where interfering with the natural world is essentially problematic, and most medical interventions are seen as unnecessary and intrusive.

3 Depathologising belief

Part 2 is about changing our pre-theoretical conception of delusion to reflect the interesting work that psychologists, philosophers, and psychiatrists have done in the last thirty years—and some ideas I draw from have been around for much longer. In the philosophy of medicine, we tend to see pathology as connected with harm and with dysfunction. In chapter 5 (“Delusions and dysfunction”) I discuss the view that delusions are the product of a dysfunction and in chapter 6 (“Delusions and harm”) I ask to what extent they are the cause of harm, for the speakers and for their communities.

My fairly idiosyncratic view is that beliefs are not the kind of thing that can be pathological, at least not in isolation from other things. However, I cast my reservations aside and examine the science of delusion formation. It turns out that in some models, such as the two-factor theory and the predictive coding theory, a deficit is explicitly invoked in the explanation of how delusions emerge. But I argue that in the two-factor theory the deficit may be better described as a set of biases that are widespread in human cognition, and in the predictive coding framework the deficit is not something that concerns cognitive processes as such. So, there may be something pathological lurking around, but it is not a belief.

Coming to harm, it would be disingenuous to deny that some delusional beliefs have a catastrophic impact on people’s functioning and wellbeing: for instance, some delusions of guilt seem to be directly responsible for people’s self-harming. But my main focus is trying to understand what the relationship is between the delusion and the harm. Is the delusion single-handedly causing the harm, or is it doing so in combination with other factors? Is the harm something caused by some other problem, to which the delusion is an imperfect solution? I discuss health risks, exclusion and stigma, and the delegitimization of societal institutions as possible consequences of reporting or spreading delusional beliefs.

There is nothing more counterintuitive than the view that delusions are beneficial, and in chapter 7 (“Delusions and meaning”) I tackle the potential upsides of delusional beliefs, concentrating on one of their features that is often neglected in analytic philosophy of mind: the fact that they often increase people’s sense that their lives are meaningful. The delusion can be very distressing and disruptive in the long term, but it also relieves people from the anxiety caused by uncertainty: the delusion explains a significant experience in a way that makes sense to the person who is having that experience.

Chapter 8 (“Delusions and agency”) is by far the most speculative of the book chapters, a “big picture” chapter. There is nothing I discuss there that hasn’t been said before, but the novelty lies in the attempt to combine what I regard as the best philosophical and empirical research on delusions to sketch the potential consequences of a reconceptualization of delusions. The idea that the presence of a delusion signals that there is something wrong with the person reporting it is not only a dangerous over-simplification, but it can also prevent us from exchanging ideas productively with people who have different worldviews and values in a number of different contexts. If a delusion is a rewarding explanation of personal and social realities that are problematic, then taking away the delusion won’t help us respond to the needs that gave rise to it in the first place. We all need to work to provide better explanations that satisfy our love of the truth but also our needs to belong, connect, and feel powerful and in control. In such a project, philosophers have an important role to play.