Legal Definitions - M'Naughten rule

The M'Naughten rule is a legal test used in criminal prosecutions to determine if a defendant is legally insane. The rule is named after a notorious English assassin who was tried in the early 1800s.

Under the M'Naughten rule, a defendant is considered legally insane if they cannot distinguish between right and wrong in regards to the crime they are charged with. If the judge or jury finds that the accused could not tell the difference, then there could not be criminal intent.

For example, if someone with a severe mental illness commits a crime but did not understand that their actions were wrong, they may be found not guilty by reason of insanity under the M'Naughten rule.

However, modern psychiatry and psychology have developed more comprehensive tests for lack of capacity to "think straight." These tests are used in most states either under the American Law Institute's Model Penal Code or the "Durham Rule."