'Fixed false belief' is a poor definition: a delusion does not have to be false or fixed, only relatively impervious to reasoning, and it comes out of a psychotic process, so what matters is how the belief arose and how it is held, not whether it is true or bizarre. Interview with suspension of disbelief and curious, gentle challenge, do not argue or agree, and in treatment do not work on the delusion much unless it gets in the way of the plan.
What it is
'Fixed false belief' is not enough, and the DSM-5 wording (fixed beliefs not amenable to change in light of conflicting evidence) is not a particularly good definition either. A delusion does not have to be false or fixed. It has to be relatively impervious to reasoning.
“it's not enough to say fixed false belief and by the way it's not even a uh doesn't have to be false and doesn't have to be fixed it just has to be relatively impervious to reasoning”
16:02What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Also said in 1 more episode
“then dsm5 they realized that that didn't work and it's just fixed beliefs that are not amenable to change in light of conflicting evidence which isn't a particularly good definition”
55:31Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 The cleanest definition: you can locate a medical condition that responds to medical treatment, the belief is not part of the person's baseline belief system, and it was not acquired through normal rational, cultural or social avenues.
“The cleanest definition, again, is that you can locate some kind of a medical condition that responds to medical treatment, is not part of the person's baseline belief system, and that the belief is not acquired through normal rational, cultural, or social avenues”
36:14Lindsay Clancy Trial: A Forensic Psychiatrist Explains Psychosis, Malingering, & the Insanity DefenseSep 2026 A delusion is a pathological belief that comes from a psychotic disorder. So identify the psychotic style of thinking first, and test it.
“A delusion is a pathological belief that comes from a psychotic disorder. So you have to identify the psychotic disorder first. You have to identify the psychotic style of thinking first and also test it”
51:22Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 You cannot define a delusion by its truth value: you can be delusional about something and be right. If a man's jealous delusion is built on nothing, it does not matter whether his wife happens to be cheating.
“it doesn't matter if the man's wife has actually happened to be cheating on him at the time, right? The reality status of that belief doesn't make it a delusion”
37:16Lindsay Clancy Trial: A Forensic Psychiatrist Explains Psychosis, Malingering, & the Insanity DefenseSep 2026 Also said in 1 more episode
“You can't define a delusion based on its truth value, first of all. Because you can be delusional about something even if you're right about it”
50:25Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 Two-factor theory: you need a strange experience, and a second problem that prevents the idea from going away.
“there's actually two disorders that need to take place in order for it to manifest. One, you need to have the strange experience. And two, you need a second disorder that prevents that idea from going away”
40:36Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 Biases that build into delusions include a bias against disconfirmatory evidence (less inclined to give an idea up) and a jumping-to-conclusions bias (accepting a hypothesis on minimal evidence, seeing something once and generalizing it).
“The first one I already mentioned, biased against disconfirmatory evidence. Basically, you're just less inclined to give an idea up”
47:33Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 Also said in 1 more episode
“Another factor that contributes jumping to conclusions bias. These are people who accept hypotheses on minimal evidence, so they can see something happen once and generalize it to everyone very easily”
47:56Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 The longer the processing of the world is off, the more beliefs get chipped away. An hour of psychosis may knock off some unimportant beliefs; longer reaches deeper.
“The longer that you're having a dysfunction in the way that you're processing the world, the more you're chipping out the beliefs. So if you're in psychosis for an hour, it's probably enough incorrect information going in that you might knock off some of the beliefs that aren't that important”
34:41Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024
How we diagnose it
Do not rate a belief by how bizarre it is, because truly psychotic people can have ordinary, non-bizarre delusions. What is left is how the person came to the belief.
“I don't think rating it based on how bizarre it is is good either because truly psychotic people can have ordinary non-bizarre delusions. So what's left? I think what's left is how did this belief come up? How did this person come to the belief”
23:03What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Do not take statements at face value. Ask how they came to understand this to be true, what experiences led to it and when they started to believe or suspect it, and how they respond to alternatives. How did you come to understand that you are Jesus Christ?
“Ask them, how is it that you came to understand this to be true? What experiences and when did you start to believe this, or suspect it at least”
25:21What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Also said in 1 more episode
“you can't take statements at face value. You really have to investigate where they come from, how they respond to alternative things, where it came from originally. How did you come to understand that you're Jesus Christ”
54:01Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 The more it arrives as a sudden, quasi-religious insight into a strange or highly valued idea, the more likely it comes from a psychotic disorder.
“The more sudden religious insight, basically, you have into a strange idea or a very valued idea, the more likely it is to be from a psychotic disorder”
29:17What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 With the strongest delusions there is a short circuit of reasoning: outside information does not get absorbed and processed. A patient who can take in what you say and consider alternatives is not showing that.
“You often don't see that in severe psychosis. You often don't see that for the strongest delusions. There's almost a short circuit of reasoning. Any outside information doesn't get absorbed in and processed in the thinking”
39:40What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Do not accept a general account. Have them imagine the exact last time, rewind to the moment before the idea came, and walk you through it step by step, at a hallucinatory level of detail.
“I want you to imagine the exact last time you did this and I want you to rewind to the moment right before you got the idea for it and walk me through it step by step. Hallucinatory level of detail”
36:28What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Measure not only how often the beliefs bother them but how much they really believe them, and whether it could be something else. That sometimes shows the source of the belief.
“I not only measure frequency of being bothered by or perceiving delusional beliefs, I also will ask, how much do you really believe that? Could it be something else that shows you sometimes the nature, the source of the apparently delusional belief”
14:30The Treatment Frame in Action: Lessons from ‘I Fell in Love with My Psychiatrist’Sep 2025 Patients with mainly delusions and hallucinations often do not tell you about the hallucinations, or do not see them as hallucinations, so all you are left with is the delusions.
“for people who have primarily delusions and hallucinations without negative symptoms or disorganization, Many of them will not tell you about the hallucinations or they don't perceive the hallucinations to be hallucinations. So all you're left with is delusions”
13:39What is Psychosis? Look at the DSM, Common Mimics, and a Framework for the DifferentialJan 2026
What it gets confused with
An overvalued idea. A rigid theory about one's own illness puts overvalued idea at the top of the differential: people get all kinds of wild theories about their illnesses.
“The first thing that comes to mind, top of the differential for me, is overvalued idea. Why? It's a theory about... his illness. And people get all kinds of wild theories about their illnesses”
33:48What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Mania can mimic psychotic features: fast, distractible, rushing thoughts and speech have been described as thought disorganization.
“even bipolar mania can mimic psychotic features uh the speed of distractible thoughts, rushing thoughts and speech can appear and has been defined in the literature as thought disorientation”
7:11What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Substance-induced and mood-induced delusions are still in the psychotic realm. They are just non-chronic.
“I would say that category two and three, the substance induced and the mood induced, I would still consider those within the psychotic realm. It's simply that they're from a non-permanent or non-chronic is the better word”
18:35What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Religious and cult beliefs need care: people who join new religions and cults tend to have more psychosis, more mental illness and more cluster A traits.
“people who subscribe to new religions and cults tend to have more psychosis. They tend to have more mental illness. They tend to be more cluster A, okay”
23:39What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026
Interview stance
Bring the same suspension of disbelief you would to a film about blue aliens. You are not sitting there skeptical.
“you need the same suspension of disbelief that you might have watching the new Avatar movie, you know, Blue Aliens. You're not sitting there skeptical”
11:44Detecting Subtle Signs of Psychosis: Assessment of Voices, Delusions, and PsychosisFeb 2026 Challenge, but not as a true challenge: with the air of disbelief of someone who really wants to understand more and believe.
“The way you should challenge in a clinical interview is not a true challenge. I think it should be with the air of disbelief of someone who really does want to understand more and believe”
13:56What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Build your calibration by also probing, not meanly, the deeply held beliefs of people without psychotic disorders, not just testing delusions.
“You can't just limit yourself to asking people about their delusions and testing them under delusions. You have to also test the deeply held beliefs, not in a mean way, but you should, you know, poke at and go into some death on the deeply held beliefs of people who are without psychotic disorders”
52:48Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024
Pitfalls
Do not take what patients say as an accurate picture of their inner state. Someone with schizophrenia may start denying the delusion mid-interview because they can still read your social judgment, and people with chronic psychosis learn not to talk about certain things. That is social learning, not remission.
“in true psychotic disorders, is that sometimes in this discussion, somebody with schizophrenia will actually start to deny that they believe the delusion. Uh, because they, their ability to detect your social judgment is not impaired”
26:29What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 Also said in 1 more episode
“what a lot of people with chronic psychosis will do from any etiology, well, they'll just socially learn that you can't talk about certain things without people looking at you”
39:37Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 Responses to treatment differ. Some patients, once antipsychotics stop the delusional perception, say they remember feeling that way but it seems strange now.
“some people, when you give them antipsychotics and they stop having that delusional perception anymore, they go like, well, I remember feeling that way about it, but that just seems strange now”
41:40Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024
Talking to patients
Do not argue with delusions, and do not agree with them. Living in the patient's world is not agreeing with it.
“Don't argue with the delusions, but also don't agree with the delusions. Right. You have to keep in mind that when you live in the world of the patient, you're not. agreeing with the delusions necessarily”
14:37Detecting Subtle Signs of Psychosis: Assessment of Voices, Delusions, and PsychosisFeb 2026 Rather than telling a patient something is not real, ask whether they are willing to consider an alternative interpretation. You might suggest it, even strongly.
“i don't think i would ever say um not purposefully to one particular patient that's not real or that isn't reality i might suggest it even strongly uh most of the time it would be to ask them if they're willing to consider an alternative interpretation as reality”
14:00The Treatment Frame in Action: Lessons from ‘I Fell in Love with My Psychiatrist’Sep 2025 Unless it directly interferes with a key or emergent part of the treatment plan, do not work on it much. Acknowledge that it is there, and if it distresses them, talk a little about that.
“unless it's directly interfering with a very key or emergent part of the treatment plan, you shouldn't work too much on it. Acknowledge that it's there. If the patient is distressed by it, you can talk a little bit about that”
43:35What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026
It also comes up on
- Substance-induced psychosisHeavy methamphetamine use can cause so much disorganization and delusion that, even after stopping, the person looks exactly like someone with schizophrenia. A paranoid delusional belief system that began on methamphetamine can persist after the perceptions that fed it stop.
- AntipsychoticsApply loose rules for delusions without much experience of severe psychotic disorders and you may prescribe a lot of unnecessary antipsychotics.
- Forensic psychiatryA trauma met through a delusion or hallucination is technically not objectively threatening, but someone who cannot tell it from reality is, in effect, objectively threatened.
- MethamphetamineMeth can cause so much disorganization, delusions and odd belief systems that, even if the person stops using, they look exactly the same as someone with schizophrenia.
- Overvalued ideasDo not argue with overvalued ideas or delusions, or challenge them head on. Some ways of framing a belief keep you stuck and others give you a chance to progress, so choose the frame that lets you keep working. This applies broadly, including to how patients understand themselves.
- PTSDUnusual routes exist. A delusion or hallucination is not objectively threatening, but most people who could not tell it from reality would be threatened. And in forensics, people can develop PTSD from being the assailant.
- PTSDReserve 'delusions', 'hallucinations', 'negative symptoms' and 'disorganization' for primary psychotic disorders. For trauma and personality syndromes say reported voices, fear or hypervigilance, and overvalued idea or inflexible belief.
- PsychosisIn the DSM, psychosis is more than delusions and hallucinations: it includes disorganized speech, disorganized behavior and negative symptoms. Catatonia sits nearby but is not only seen in psychosis.
From these episodes
- Lindsay Clancy Trial: A Forensic Psychiatrist Explains Psychosis, Malingering, & the Insanity DefenseSep 2026 · 2 points
- Detecting Subtle Signs of Psychosis: Assessment of Voices, Delusions, and PsychosisFeb 2026 · 2 points
- What Makes a Belief a Delusion? Delusions, Thought Disorder, the TALD ScaleJan 2026 · 13 points
- What is Psychosis? Look at the DSM, Common Mimics, and a Framework for the DifferentialJan 2026 · 1 point
- The Treatment Frame in Action: Lessons from ‘I Fell in Love with My Psychiatrist’Sep 2025 · 2 points
- Psychosis: History, Delusions, Diagnosis, Theories, and Modern CareNov 2024 · 11 points
Every point above is something said on the Psychofarm podcast, with the words as spoken and a link to the moment in the episode. It is education, not medical advice, and an episode reflects what we thought when we recorded it.