Johnson [2007] EWCA Crim 1978

Key point

Knowing that an act was wrong under the M’Nagthen rules for the defence of insanity meant that the defendant knew that his act was illegal, not that it was morally wrong.


  • D, who had schizophrenia stabbed people while he was subject to delusion
  • Psychiatrists agreed that D knew the nature of his acts and that it was against the law, but one raised the point that he might not be aware that it was morally wrong
  • The High Court judge ruled that the defence of insanity could not be raised as D was aware his act was legally wrong
  • D appealed on basis that the ruling was wrong

Held (Court of Appeal)

Appeal dismissed; knowledge of illegality was the sole criterion of knowing what was wrong under the M’Naghten rules.


In an opposite case where D knows what he was morally wrong but not that it was illegal, the insanity defence would not apply

Incapacity Cases
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