What Is Schizophrenia?

Schizophrenia is a collection of seemingly unrelated symptoms, with no one defining characteristic. 

DSM-V - one positive symptom enough for diagnosis

ICD-10 - two or more negative symptoms enough for diagnosis 

Positive symptoms are symptoms that involve abnormal additional experiences, out of the ordinary (e.g. hallucinations and delusions)

Hallucinations

A hallucination is a sensory experience where one perceives things that have no basis in reality (e.g. hearing voices or seeing things that are not there)

Delusions

A delusion is a firmly held irrational belief, even in the face of contradictory evidence. (e.g. paranoid delusion, delusions of persecution/grandeur)

Negative symptoms of schizophrenia involve an absence of experiences that people normally have (e.g. avolition and speech poverty)

Avolition

Avolition is a severe and persistent lack of motivation to carry out everyday tasks (e.g. work, hobbies and personal care). 

Speech poverty 

Speech poverty is a reduction in amount of and quality of speech, especially spontaneous speech (e.g. using minimal speech/disorganised speech)