9. Mental conditions, intoxication and mistake

Abstract

This chapter considers the most commonly occurring ‘mental condition defences’, focusing on the pleas of insanity, intoxication and mistake. The common law historically made a distinction between justification and excuse, at least in relation to homicide. It is said that justification relates to the rightness of the act but to excuse as to the circumstances of the individual actor. The chapter examines the relationship between mental condition defences, insanity and unfitness to be tried, and explains the Law Commission’s most recent recommendations for reforming unfitness and other mental condition defences. It explores the test of insanity, disease of the mind (insanity) versus external factor (sane automatism), insane delusions and insanity, burden of proof, function of the jury, self-induced automatism, intoxication as a denial of criminal responsibility, voluntary and involuntary intoxication, dangerous or non-dangerous drugs in basic intent crime and intoxication induced with the intention of committing crime.