M'Naghten's Case
10 CL & F. 200, 8 Eng. Rep. 718 (1843)

  • M'Naghten believed that he was the victim of an international conspiracy, involving the Pope and the British Tory government. He went to London and shot a guy he thought was the Prime Minister.
  • M'Naghten was arrested and charged with murder.
  • The British Trial Court found M'Naghten not guilty by reason of insanity.
    • M'Naghten was then forcibly institutionalized for the remainder of his life under the Criminal Lunatics Act of 1800.
  • The case caused a public outcry in England. The House of Lords sat down and developed a set of rules (known as the M'Naghten Rules) for when insanity can be used as a defense. These rules include:
    • Presumption of Sanity:
      • Sanity is a rebuttable presumption and the burden of proof is on the party relying upon it; the standard of proof is on a balance of probabilities, that is to say that mental incapacity is more likely than unlikely.
    • Disease of the Mind:
      • It doesn't have to be a 'brain' condition, it could be "any disease which produces a malfunctioning of the mind." But it must be a 'disease', the defense can't be used if you just get carried away.
    • Nature and Quality of the Act:
      • The defense of insanity covers situations where the defendant doesn't understand what they a physically doing.
    • Knowledge that the act was wrong:
      • The defense of insanity covers situations where the defendant knows what they are doing, but can't understand that it is a criminal act.
    • Strict Liability:
      • Insanity is not a defense for crimes of strict liability.
  • This case laid out the basic common-law principles for the defense of insanity.
  • The M'Naghten Test is just a cognitive test. It says that a defendant is not responsible for his criminal conduct if, at the time of the conduct, as a result of a mental disease or defect that he:
    • Did not know the nature and quality of the act he was doing, or
    • Did not know what he was doing was wrong.
  • The Model Penal Code 4.01 test has a both a cognitive prong and a volitional prong. It says that a defendant is not responsible for his criminal conduct if, at the time of the conduct, as a result of a mental disease or defect, he lacked substantial capacity to:
    • Appreciate the criminality (aka wrongness) of his conduct, or
    • Conform his conduct to the requirements of the law.
      • So, a kleptomaniac who knows that stealing is wrong, but can't help himself, would be entitled to an insanity defense under the Model Penal Code, but not under M'Naghten Test.