Psychosis is a general term referring to the loss of the ability to interact with reality, sustained by thinking that is no longer structured according to logical and functional patterns. It may or may not be associated with alterations in incoming signals, that is, visual, auditory, olfactory, or somatic sensations (illusions, hallucinations). Psychosis is therefore a state of “alienation,” that is, exclusion from interactions with the environment because the person lives in their own world, detached from any shared logic of communication.
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 thinking. However, it does not merely 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 a 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 thinking is “disturbed.”
Let us begin 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, that is, theoretically “it could be true.” What matters is how the person expresses this belief: how they began to think about it and what led them to become convinced of such a thing.
Normal thinking, regardless of whether it begins with an intuition or with the observation of external elements, then proceeds through verification in order to reach a judgment. Usually, if the association between the elements and the thought is understandable according to some form of logic—emotional, conceptual, or based on direct past experience—the person concludes that their thought is true. Otherwise, they leave it unresolved or abandon it, especially when the associations between ideas are bizarre or do not seem realistic on other grounds.
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. Moreover, delusions often contain elements that function as a kind of logical black hole because they are not clearly defined. 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 inherently implausible, 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 hypotheses that a person enjoys entertaining. Conversely, there are ideas and ideologies regarded as respectable and socially acceptable—for example, religious beliefs—that are not logically linear or rationally understandable. Yet adherence to a religion is not in itself evidence of delusional thinking, because what lies at the center of religious practice is not adherence to the logic of thought itself, but rather a series of meanings, functions, and representations of reality.
A delusion is therefore fundamentally defined by an “un-derived” structure, that is, a relationship between premises and conclusions that is logically incomprehensible. For example: “My wife is cheating on me because cars pass by the house, and it is her lover who is checking whether I am there.” This reasoning is illogical because the premise—that the lover is driving past the house—already presupposes that the affair is true, whereas it is presented as evidence for the affair.
Delusional thinking is deductive: the person already knows that something is true, and therefore interprets everything else accordingly. Normal thinking, by contrast, includes a phase of verification.
The second characteristic of a delusion is the awareness of reality, which in a delusion is automatic. A thought is experienced as real at the very moment it is formulated. Awareness is not the result of an ongoing comparison that can always be modified; rather, the notion emerges already endowed with the status of truth.
When hallucinations are associated with delusions, a person might say, for example, “They want to kill me because I hear voices threatening me.” Someone who suddenly began hearing voices would normally first be concerned about the possibility of hallucinations, or try to understand where the voices were coming from. Automatic acceptance of their content is a sign that, in addition to the hallucinations, thinking itself is disturbed.
Sometimes certain hallucinations—for example, “There are flames inside my brain that are burning it”—are not merely sensations expressed in a figurative or colorful way. They may consist of a hallucination (a sensation of burning in the head) accompanied by the conviction that there are actual flames inside the brain that are burning it.
Delusions are present in various psychiatric disorders. In some, they are the main feature (the 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 may also be produced by external substances, such as medications or drugs. In some cases, delusions are produced as part of a stimulating or altered experience, for example with hallucinogens, hashish, or phencyclidine.
Delusions can be distinguished according to how they arise:
Perceptual delusions, which begin with seeing or hearing something that is interpreted in a delusional way—for example, a person I do not know touches their hair, and I think this is a signal meant to tell me that I am in danger.
Intuitive delusions, which begin with an internal thought, such as suddenly realizing that I am the reincarnation of Jesus and have a mission to fulfill.
Representational delusions, which begin with a memory—for example, recalling a congratulatory or good-luck 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 possessing secret and valuable information, to having invented something new and brilliant); depressive delusions (being ruined, being responsible for some event, having a fatal illness); somatic delusions (being infested with parasites, having various diseases, or no longer having certain parts of the body); erotomanic delusions (believing that someone is in love with us); and so on.
Obviously, none of these contents, considered by themselves, constitutes an alteration of thought. What is required is the presence of the two characteristics described above: the lack of a logically understandable derivation between premises and conclusions, and the loss of a normal awareness of reality.