Psychosis is a generic term used to describe the loss of the ability to interact with reality, sustained by thinking that is no longer structured according to logical and functional lines. It may or may not be associated with alterations in incoming signals, that is, visual, auditory, olfactory, and somatic sensations (illusions, hallucinations). Psychosis is therefore a state of “alienation,” meaning exclusion from interactions with the environment because the person lives in their own world, detached from any communicative logic.
The best-known psychotic symptoms are hallucinations and delusions, but there are others as well, such as the loss of affective resonance and the loss of the connection between thought, feeling, and initiative.
A delusion is the most common psychotic symptom. Literally, it means a thought that does not follow the normal line of reasoning. It does not simply produce fantasies, hypotheses, or intuitions to be verified later, but rather automatic convictions that are independent of any verification.
When someone expresses an idea or belief, we cannot know with certainty whether that belief is justified or not. Certainly, we can judge whether the belief is common or bizarre, strange or normal, but this is not sufficient to establish whether the thought itself is “disturbed.”
Let us start with an example of a delusion. Suppose a person says, “They want to kill me,” and also identifies who they are and why they want to do it. The thought itself is plausible, meaning that theoretically it “could be true.” What matters is “how” the person expresses this belief: how they came to think it, and what led them to become convinced of something like this. Normal thinking, regardless of whether it begins with intuition or with observation of external elements, proceeds through a process of verification in order to arrive at a provisional final judgment (even a convinced person is convinced “until proven otherwise”). Usually, if the association between the elements and the thought is understandable according to an emotional, conceptual, or directly experienced logic, the person concludes that the thought is true. Otherwise, they keep it in suspension or abandon it, especially when the associations of ideas are bizarre or do not appear realistic on other levels.
Thus, if someone thinks, “They want to kill me because they are wearing red shoes and therefore they are demons,” the structure of the thought does not logically support the belief. Furthermore, delusions often contain elements that function as a kind of logical black hole because they have no clear definition. For example, “demons,” “entities,” and “deities,” in relation to shared reality, remain indefinable: their attributes may be described, but their substance cannot be established.
A delusion, therefore, is not simply a strange or bizarre content. “They want to kill me” is not in itself an implausible statement, just as—using another example—“My wife is cheating on me” is not inherently implausible. Of course, many delusions are also implausible in terms of their content, for example, “I am in contact with extraterrestrials,” but it would be a mistake to judge someone as delusional solely on the basis of the content of their ideas.
In reality, many of us have strange, bizarre, and implausible thoughts that reflect fantasies or that are not absolute convictions, but rather hypotheses that a person enjoys entertaining. Conversely, there are ideas and ideologies that are considered worthy and socially acceptable (for example, religious beliefs) that are not logically linear or rationally comprehensible. Yet adherence to a religion is not in itself a sign of delusional thinking, because what lies at the center of religious practice is not simply adherence to the logic of a particular thought, but a series of meanings, functions, and representations of reality.
A delusion is therefore fundamentally defined by an “underivable” structure, meaning that the relationship between premises and conclusions is logically incomprehensible. For example: “My wife is cheating on me because cars pass by my house, and it is her lover checking whether I am there.” This reasoning is illogical because the premise—the lover driving past the house—already presupposes that the affair is real, while it is simultaneously presented as evidence that the affair is real.
Delusional thinking is deductive: the person already knows that something is true, and everything else is interpreted accordingly. Normally, however, thinking includes a phase of verification.
The second characteristic of a delusion is the consciousness of reality. In a delusion, this consciousness is automatic: a thought is experienced as real at the moment it is formulated. Consciousness of reality is not the result of an ongoing and potentially revisable comparison with evidence, but rather a notion that arises already as true.
In summary, a delusion is a thought that, from the outset, does not admit contradictory evidence, and that is conceived in an underivable and deductive manner. Its content and associated symptoms may vary.
When hallucinations are associated with delusions, a person might, for example, say: “They want to kill me because I hear voices threatening me.” Someone who suddenly heard voices out of nowhere would first be concerned about having hallucinations or would try to understand where they were coming from. Automatic acceptance of their content is a sign that, in addition to the hallucinations, thought itself is also disturbed.
Sometimes certain hallucinations, such as “There are flames inside my brain burning it,” are not merely sensations expressed in a figurative or picturesque way. They may consist of a hallucination—a burning sensation in the head—combined with the conviction that there are actual flames inside the brain that are burning it.
Delusions occur in several psychiatric disorders. In some, they are the main feature (so-called delusional disorders); in others, they are one of the principal symptoms (schizophrenia); in others, they may occur and represent a sign of severity (manic-depressive psychosis). Delusions can also be produced by external substances, such as medications or drugs. In some cases, delusions are produced as part of a stimulating experience, for example with hallucinogens, hashish, or phencyclidine.
They can be distinguished as follows:
Perceptual delusions: these begin with seeing or hearing something that is interpreted in a delusional manner. For example, a person I do not know touches their hair, and I think this is a signal intended to make me understand that I am in danger.
Intuitive delusions: these begin with an internal thought, such as suddenly intuiting that one is the reincarnation of Jesus and has a mission to accomplish.
Representational delusions: these begin with a memory, such as recalling a congratulatory phrase spoken by a friend the previous day and realizing that it was actually a warning that I am in mortal danger.
Delusions can also be classified according to their content:
Grandiose/megalomanic delusions: ranging from believing that one has special powers, to believing that one possesses secret and valuable information, or that one has invented new and brilliant things.
Depressive delusions: believing that one is ruined, responsible for some catastrophic event, or suffering from a fatal illness.
Somatic delusions: believing that one is infested with parasites, has various diseases, or has lost parts of one’s body.
Persecutory delusions: believing that one is being spied on, controlled, manipulated, or disturbed through signals, interference, curses, or other harmful influences; believing that one is being poisoned or is the object of excessive interest from other people.
Erotomanic delusions: believing that someone is in love with us.
A delusion can become increasingly complex over time, but there is usually a moment when the fundamental idea is first conceived, perhaps without being discussed because its details are not yet clear.
During the phase in which a delusion emerges—or re-emerges after having previously disappeared—there is often a feeling of perplexity, as though the usual reference points of reality were no longer present or were beginning to acquire different meanings. This is a genuine embryonic stage of delusion, in which the person senses that “something is about to happen” or that “there is something I cannot understand,” a truth or revelation that has not yet taken on any definite details. This condition is called a pre-delusional state, or Wahnstimmung.
One of the most common ways of describing a delusion is to say that it is “lucid” or not lucid. In reality, if by “lucid” one means adherence to reality, then a delusion is, by definition, never “lucid.” If, on the other hand, one means that the person’s behavior is organized in the same way as that of a non-delusional person, this is common.
At the very least, behavior may remain organized in relation to the goals the person is trying to achieve at that particular moment (for example, buying something, attacking someone, traveling, and so on).
Another term commonly used to describe a delusion is “dissociative state.” In contemporary classification, this term would actually refer to a different type of disorder, but as a word it conveys the idea of “alienation.”