Conventional psychiatry has emphasized the genetic roots of psychosis based on the claim that twin and other studies show that schizophrenia is 80% heritable, which means that 80% of the cause is genetic.

My interest in the psychological roots of psychosis has both personal (my brother Andrew committed suicide) and professional origins (I was trained in a behaviorist approach to psychology which - whatever its limitations - at least taught me to see human behavior in its social context).

Since the Second World War, rates of common mental illness (depression and anxiety) have been increasing in the industrialized nations, whereas rates of recovery from severe mental illness have not improved despite the availability of apparently effective therapies such as antipsychotic drugs.

If we are to believe the evidence from clinical trials there are many effective pharmacological and psychological treatments for mental illness. Epidemiological data, on the other hand, says otherwise.

The only way you can estimate environmental influences is by measuring them.

There is almost no evidence that diagnoses such as 'schizophrenia' and 'bipolar disorder' correspond to discrete entities ('natural kinds' in the language of philosophy).

There are many kinds of adult adversities that can provoke severe psychological distress, including debt and unemployment, dysfunctional marital relationships and occupational stress. The reality is that the social causes of mental ill-health are all around us.