Imagine that you are taking a walk in your hometown when you notice a dog on the steps of a Catholic church. While you pass the front of the church, the dog gets up on his hind legs. Then he moves his front paw forward. What do you make of this? Probably nothing. But what if you felt that the dog’s action was meant for you? Maybe you would start thinking about other events involving churches that you witnessed recently. Maybe the previous encounters were also meant for you and led up to today’s event. Maybe the dog was trying to communicate something. Maybe he was delivering a message from God, revealing that you were chosen to carry out an important mission.
The hypothesis that the dog is a messenger from God is far-fetched, you can grant that. If one of your friends had come up with such a story you would not believe her, and so it is not a surprise for you if your friends do not believe you when you tell them. But you just know it is true. It explains everything. Knowing why the dog behaved as he did dissolves at last the anxiety and uncertainty that had become a constant feature of your everyday experiences: feeling that something important was about to happen, and the dread of not knowing what it was. When you realize that the dog is delivering a message from God, you feel relieved and empowered. God has found a secret and effective way to communicate with you.
What we call “schizophrenia” is often a severe and disabling condition. In the context of schizophrenia, if you are about to endorse a delusional thought (“God is trying to communicate something important to me through this dog”), then you are likely to have had anomalous experiences similar to the one described above (adapted from the one originally presented by Schneider in his 1959 Clinical Psychopathology). Prior to witnessing the event that led you to endorse a delusion, a number of events had become especially significant to you in a way that you did not fully understand and that caused considerable anxiety to you (this is called the prodromal stage of psychosis). When the delusional hypothesis emerges to explain a new event, it is compelling as it seems to shed light on your previous experiences as well, and on the questions they raised (“Why do I feel that the dog’s actions are so important? Was he saluting me? Could his actions mean something?”).
Delusions can differ in content. Some are very hard to believe, almost absurd (“I’m dead,” “My wife has been replaced by an impostor,” “My neighbor is inserting thoughts into my head”). Other delusions are extreme versions of very common beliefs. In delusions of jealousy you believe that your partner is unfaithful; in delusions of grandeur you believe that you are a misunderstood genius; in erotomania you believe that someone is secretly in love with you; and in delusions of persecution you believe that others want to cause you harm.
Whether outlandish or mundane, the delusion persists despite contrary evidence and external challenges, and often conflicts with other things you believe. Delusions are a clear sign that something is wrong — they are regarded as a paradigmatic instance of irrationality in the psychological literature, and are the mark of madness in popular culture and fiction. They can lead you to lose touch with reality, make bad decisions, and endorse other implausible beliefs. They can impair your capacity to function well by making it difficult for you to participate in family life, foster relationships, continue your studies, keep your job, and generally pursue your life goals. Delusions are a source of preoccupation, social withdrawal, and depression. As Roberta Payne puts it in her wonderful memoir, Speaking to My Madness, a life with schizophrenia can be a poor imitation of a life.
It is no surprise, then, that delusions have a bad press. My question today is whether delusions are the problem, rather than the beginning of a solution. Some psychological studies show a positive impact of delusions on wellbeing and meaningfulness , suggesting that forming delusional beliefs may be adaptive. The human brain is largely a predictive machine: it allows you to predict future events on the basis of your current experiences. Experiences with heightened significance may disrupt the way you learn and interact with your environment, and cause serious concern and anxious expectation: what will happen next?
By experiencing random events as especially significant you feel puzzled and unsettled until you find an explanation for those events. When you are unable to understand why the world around you has changed, the delusion may temporarily relieve anxiety by providing an explanation for events whose apparent significance is mysterious, and the sense of heightened significance becomes less threatening. In the case of delusions such as the one about the dog raising his paw to deliver a message from God, the delusion may also enhance the sense that your life is meaningful and make you feel engaged in a worthy project. When the conviction in the delusion fades, then the sense of meaningfulness decreases, and so does your wellbeing .
This suggests that delusions can have benefits of some sort. By making your life more meaningful and coherent, the delusion dissolves negative feelings about yourself or your situation, thereby reducing anxiety and stress. Anxiety and stress have negative consequences for your capacity to acquire knowledge because they compromise (among other things) attention and concentration, and undermine the interactions with your physical and social environment. It would seem that delusions have epistemic benefits: by providing an explanation of anomalous experience that makes you feel better about yourself they indirectly boost your capacity to acquire knowledge and overcome the effects of the prodromal stage of psychosis.
The idea that beliefs that defy evidence can be good for you is certainly not new, when the benefits are cashed out in psychological or biological terms: some implausible beliefs can enhance your wellbeing and improve your chances of success. So-called positive illusions, that is, excessively positive beliefs about yourself or your future prospects (such as “I’m a good public speaker,” “I’m smarter than the average person,” “My cancer has been successfully treated,” “My marriage won’t end up in divorce”) can translate into better chances to perform well in a variety of tasks requiring self-confidence, to maintain satisfying relationships, and to have a long and healthy life. But the view that there is a trade-off between enhancing health and wellbeing and promoting knowledge seems too simplistic. Beliefs that defy the evidence can be good for knowledge too. When beliefs have psychological benefits for you, they also have good consequences for your capacity to acquire knowledge.
There may also be ways in which adopting a delusion promotes knowledge independently of its psychological benefits. Learning is the outcome of the process by which the brain predicts the future on the basis of present experiences, and it is impaired when random events appear highly significant. As Mishara and Corlett  argue, when your attention is captured by events that do not deserve it, other potentially significant events are neglected as a result. By offering an explanation for many (only apparently) significant events, the delusion releases attention that can be more usefully employed in other ways. You can stop worrying about the dog’s unusual behavior if you have come to the conclusion that the dog was the means by which God chose to communicate with you. And you can focus your attention on other events, becoming more alert to what is happening around you. A more balanced allocation of cognitive resources, attention included, guarantees that you continue to update your model of the world on the basis of the stimuli you receive. By enabling learning to resume, the delusion can be regarded as having benefits for knowledge that do not depend on increased wellbeing.
The idea that in some specific contexts even wildly false beliefs can promote knowledge is counterintuitive, just like the idea that a morally dubious act can have good moral consequences. But the analogy can help us. In some circumstances, an apparent offense can prevent a worse outcome from occurring. For instance, you stop a terrorist from detonating a bomb by shooting his leg and making him fall. Shooting people is bad. But stopping the terrorist may be the right thing to do in the circumstances, especially if the bomb is likely to harm other people. If less violent means of stopping the terrorist are not available to you at the time, then what you do is justifiable. Similarly, if even wildly false beliefs can play an important function by enabling imperfect human agents to acquire knowledge in imperfect situations, that counts as a powerful redeeming feature.
This notion may apply to delusions and other implausible beliefs. Without adopting the delusion, you would be overwhelmed by anxiety, puzzled and unable to engage and learn, because you would not have an explanation for your experience. You would see the dog’s actions, have a strong sense that the experience is significant, but have no clue as to what its meaning could be, and feel lost and maybe even threatened by it. Other (far more plausible) explanations for the experience (such as “This event appears significant to me because there is something wrong with my brain”) would be less likely to enhance your sense of meaningfulness and coherence and to make you feel important and engaged. Thus, they would have fewer chances of reducing anxiety and stress. Coming to believe that you suffer from a disabling mental condition would increase your anxiety and stress, and lower your self-esteem.
Adopting the delusional explanation allows you to continue to process information effectively in a situation where your capacity to learn would be otherwise compromised. It is an emergency response in a disastrous scenario, comparable to shooting the terrorist in his leg just before he detonates a bomb that is likely to harm others. Thus, adopting the delusion may have beneficial effects on your capacity to obtain knowledge, but only with respect to a situation that is already problematic. The positive effects of the delusion may be temporary and limited in scope, and will be outweighed at a later stage due to the considerable disruption caused by the delusion. By letting the delusion shape your life, you find new sources of anxiety and stress, and you are likely to experience social isolation and exclusion as well. But despite these important qualifications, the claim that delusions have benefits for knowledge is important, and has implications for treatment.
The clinical psychologist Daniel Freeman and his colleagues  found that when you endorse a delusional belief with conviction (in the acute stage) you are not open to acknowledging that there may be other hypotheses explaining your experience. As a result of this finding, they argue that it is not always a good idea to challenge a delusion. If you cannot think of alternative explanations, there is nothing you can replace the delusion with, and thus when the delusion is challenged you may be left without any explanation for your experience. If delusions are sometimes beneficial, and enable you to resume learning in the way I suggested, then there may be an additional reason not to challenge them at the acute stage. Delusions may be playing the role of an emergency response, partially deceiving you but at the same time allowing you to continue engaging with the world around you, and potentially acquiring knowledge at a critical time.
Lisa Bortolotti is a Professor of Philosophy at the University of Birmingham. Her main research area is the philosophy of cognitive science, and in her work she has focused on the limitations of human cognition and human agency. She is also interested in the relationship between science and society and in the ethical issues emerging from biomedical research, psychiatry, reproduction, parenting, and the treatment of nonhuman animals. Her latest book is Irrationality (Polity Press, 2014).
 Delusional belief systems and meaning in life: A preferred reality?, by G. Roberts, The British Journal of Psychiatry 159:19-28, 1991.
 Sense of coherence among delusional patients: prediction of remission and risk of relapse, by M. Bergstein, A. Weizman, and Z. Solomon. Comparative Psychiatry 49:288-96, 2008.
 Are delusions biologically adaptive? Salvaging the doxastic shear pin, by A.L. Mishara and P. Corlett, Behavioral and Brain Sciences 32:530- 531, 2010.
 Why do people with delusions fail to choose more realistic explanations for their experiences? An empirical investigation, by D. Freeman et al., Journal of Consulting Clinical Psychology 72:671-680, 2004.