Discuss whether the rules governing insanity as a defence in criminal law are in a satisfactory condition. The defence of insanity is based on the M'Naghten Rules and clears the defendant of any criminal liability, they would instead be found not-guilty by reason of insanity. In M'Naghten 1843 the defendant suffered from paranoia and felt like the government were out to get him. Under this belief, he committed murder. He was found not-guilty due to his mental state and was committed to a mental hospital. The public outcry caused by this case led the House of Lords to answer many questions to clarify the law over insanity. The main rule given is that "in all cases, every man is presumed to be sane and to possess a sufficient degree of reason to be responsible for his crimes." And the definition of insanity was given as "labouring under such a defect of reason from disease of the mind as to not know the nature and quality of the act he was doing, or if he did know it, that he did not know he was doing what was wrong." "Defect of reason" means that the defendant's powers of reasoning must be impaired. I they can reason but do not then there is no defect of reason. This was decided in Clarke 1972 when it was held absent-mindedness and confusion are not defects of reason. .
In the case of insanity as a defence, "Insanity" is a legal term, not a medical one, therefore its definition is not medical either. The definition states that the defendant must be suffering from a "disease of the mind" and the law states that this can be a mental or physical disease or injury which affects the mind. For example, in Kemp 1956, hardening of the arteries was sufficient as a disease of the mind as it caused the defendant to blackout. In Sullivan 1984 epilepsy was used as the disease of the mind and it was held that it doesn't matter whether the impairment of reason is permanent, transient or intermittent.