Although there are no features that provide an unambiguous distinction between the delusions of schizophrenia and those of other psychotic illnesses, the delusions most typical of schizophrenia have an enigmatic character rarely seen in other disorders. In contrast to the delusions of affective psychosis, which usually have content consistent with the prevailing emotional state, in schizophrenia delusions often appear to reflect a fragmented experience of reality. This fragmentation is manifest in several ways.

The mental mechanism of schizophrenic delusions remains to be ascertained. It is not a lack of capacity for logical thought; rather it appears that certain ideas acquire an attribute that exempts them from the normal processes of validation. This phenomenon is illustrated by the historic case of Daniel Schreber,⁽²⁾ a high-ranking judge from Leipzig, who suffered a late-onset schizophrenic illness. After obtaining a court order for discharge from his second hospital admission he published his memoirs⁽³⁾ in a volume that includes his own account of his beliefs, and also the report prepared by the asylum director, Dr Weber, opposing his discharge. For the purpose of understanding the nature of delusions in schizophrenia, Schreber’s account is of special value because we have access to his own perceptions of his condition in addition to detailed accounts by his physician. Dr Weber reported that Schreber exhibited lively interest in his social environment, a well-informed mind, and sound judgement, while nonetheless maintaining his delusional beliefs in a manner that would accept no contrary argument. Schreber himself agreed that his beliefs were unchangeable. He believed that he had a mission to redeem the world and restore humankind to its lost state of bliss. His system of delusions included the belief that he was being transformed into a voluptuous female partner of God. He considered that his beliefs belonged to a domain that was exempt from normal logic: ‘I could even say with Jesus Christ: My kingdom is not of this world; my so-called delusions are concerned solely with God and the beyond’. Furthermore, he maintained total conviction in his core beliefs despite recognizing that his experiences earlier in his illness had been unrealistic. He stated:

Thus, in the stable phase of his illness, Schreber recognized that his earlier experiences were unrealistic and that his current beliefs defied normal logic, but appeared to regard them as exempt from the need for validation. The late onset of his illness and his high level of professional achievement are unusual for an individual with schizophrenia, and raise questions about the diagnosis. However, the fact that he eventually suffered a marked deterioration in function during his third episode of illness strongly supports the diagnosis of schizophrenia.

In many instances, the delusions of schizophrenia appear to arise from an altered experience of self. The phenomena identified by the German psychiatrist, Kurt Schneider⁽⁴⁾ as first-rank symptoms of schizophrenia (discussed in greater detail below) include several symptoms that entail an aberrant experience of ownership of one’s own thought, will, action, emotion, or bodily function, which the patient attributes to alien influence. In some cases, delusions might arise from a delusional mood, i.e. an altered sense of reality in which the current circumstances acquire an indefinable transcendental quality.

Although the delusions most characteristic of schizophrenia have an incongruous quality, it is not uncommon for schizophrenic patients to have coherent delusions that are internally consistent and produce predictable behavioural responses. In particular, coherent persecutory delusions are common, and can lead to defensive actions such barricading oneself in one’s room with blinds drawn. Ideas of reference and delusions of reference are also prevalent. For example, a patient might report that television
programmes refer specifically to him or her. In the International Pilot Study of Schizophrenia⁽⁵⁾ conducted by the World Health Organization, ideas of reference were reported in 70 per cent of cases, suspiciousness in 66 per cent, and delusions of persecution in 64 per cent.

Hallucinations in any modality can occur, but auditory hallucinations are the most prevalent in schizophrenia. Hearing voices speaking in the third person is the most specific. This experience is listed among the Schneiderian first-rank symptoms. Sometimes the content is mundane, as in the instance when a patient of Bleuler⁽¹⁾ heard a voice saying ‘Now she is combing her hair’ while she was grooming in the morning. In other instances there is an implied criticism, as in the case reported by Schneider⁽⁴⁾ of a woman who heard a voice saying ‘Now she is eating; here she is munching again’, whenever she wanted to eat.

Second-person auditory hallucinations are also common. In the International Pilot Study of Schizophrenia,⁽⁵⁾ voices speaking to the patient were reported in 65 per cent of cases. Voices might issue commands that the patient obeys. In some instances, the patient engages in a dialogue with the voices.

During the acute phase of illness, auditory hallucinations usually have the same sensory quality as voices arising from sources in the external world. In some instances the voice is attributed to a radio-transmitter implanted in the body, especially in the teeth. In the chronic phase, the voices are often recognized as coming from within the person’s own mind. Kraepelin⁽⁶⁾ reports: ‘at other times they do not appear to the patient as sense perceptions at all; they are ‘voices of conscience’; ‘voices which do not speak with words”. These experiences are pseudohallucinations, but nonetheless they are a significant feature in many cases.

In schizophrenia, visual hallucinations are less common than auditory hallucinations, but do occur. Somatic hallucinations are also relatively common, and often are associated with a delusional misinterpretation. For example, a young man reported sensations in his belly that he attributed to a snake, which he believed had crawled up his anus.

Kurt Schneider⁽⁴⁾ identified a set of phenomena that he considered were strongly indicative of schizophrenia in the absence of overt brain disease. These symptoms, listed in Table 4.3.2.1, have become known as first-rank symptoms. Schneider did not consider that the diagnosis could be made simply on the presence of one such symptom; on the contrary, he warned,⁽⁴⁾ ‘a psychotic phenomenon is not like a defective stone in an otherwise perfect mosaic’. Schneider did not define the phenomena precisely, and clinicians have interpreted his writings differently. Mellor⁽⁷⁾ formulated a precise set of definitions and found that, according to these strict criteria, 72 per cent of patients with schizophrenia exhibited at least one first-rank symptom. Applying the same criteria, O’Grady⁽⁸⁾ found that in a series of cases assessed at admission to hospital, 73 per cent of schizophrenic patients exhibited at least one first-rank symptom, while no cases of affective psychosis did. However, applying less strict criteria, O’Grady found more broadly defined first-rank symptoms in 14 per cent of patients with affective psychosis.

Three of the first-rank symptoms (voices commenting, voices discussing, and audible thoughts) involve auditory hallucinations, while the remainder entail delusional attributions to experiences or perceptions. Although Schneider himself avoided speculating on the theoretical implications of these phenomena, it is notable that most of them involve a disorder of the sense of ownership of one’s own mental or physical activity. Thought broadcast, thought withdrawal, and thought insertion reflect the experience of loss of autonomy over thought, while made will, made acts, made affect, and somatic passivity reflect loss of autonomy over action, will, affect, and bodily function.

Mellor⁽⁷⁾ emphasizes that there are two aspects to these phenomena: the experience of loss of autonomy and the delusional attribution to alien influence. As an illustration of made acts, Mellor reports a patient who reported that his fingers moved to pick up objects ‘but I don’t control them … I sit there watching them move, and they are quite independent, what they do is nothing to do with me. I am just a puppet … I am just a puppet who is manipulated by cosmic strings’. To illustrate made affect, Mellor quotes a young woman: ‘I cry, tears roll down my cheeks and I look unhappy, but inside I have a cold anger because they are using me in this way, and it is not me who is unhappy, but they are projecting unhappiness into my brain’.