Schizophrenia is a psychotic disorder that lasts for at least six months and includes at least one month of active phase symptoms. The characteristic symptoms of schizophrenia involved a long range of cognitive and emotional dysfunction, this include perception, inferential thinking, language and communication, behavioral monitoring, affect, fluency, and productivity of thought and speech, hedonic capacity, volition and drive and attention. No single symptom is pathgnomonic to schizophrenia, in other words no single symptom is identified only with schizophrenia. .
In order to prevent over-diagnosing of schizophrenia, the DSM-IV has a list of diagnostic criteria for schizophrenia. Characteristic symptom, which is criterion A, can be divided into positive symptom (A1 to A4) and negative symptom (A5). The positive symptoms include delusion (A1), which are erroneous beliefs that usually involve a misinterpretation of perceptions or experience. Persecutory delusions are most common; the person believes he or she is being tormented, followed, tricked or spied on, or ridiculed. There is an also referential delusion whereby the person believes that certain gestures, comments, passages from books, newspapers, song lyrics, or other environmental cues are specifically directed to him or her. The next positive symptom is hallucination (A2). These may occur in any sensory modality, but auditory are most common. Auditory hallucinations are usually experienced as voices that are perceived as distinct from a person's own thoughts. Disorganized speech (A3) occurs in many different ways, the person may "slip off track" from one topic to another (derailment or loose association), or the person may answer questions with obliquely related or completely unrelated responses. In rare cases, speech may also be severely disorganized to the point of incomprehensibility and resembles aphasia in its linguistic disorganization (incoherence and word salad).