the McNaughten RulesMc·Naugh·ten Rules, the /məkˈnɔːtn ˌruːlz/, M'Naghten Rules, the the rules in English law which say that, if it can be proved that someone did not know what they were doing when they carried out a crime or did not know that it was wrong, then they can plead insanity (=give madness as an excuse for their actions). The rules were established as a result of the case of Regina v. McNaughten in 1843.