Which rule states that a person is not criminally responsible if unable to distinguish right from wrong due to mental illness?

The M'Naughten rule is a legal standard used to determine whether a defendant can be held criminally responsible for their actions when mental illness is in question. Under this rule, a person may be deemed not responsible for a crime if, at the time of committing the act, they were suffering from a severe mental disorder and therefore unable to understand the nature of their actions or distinguish right from wrong.

This standard places the emphasis on the cognitive ability of the individual at the time of the offense. For example, if a person was experiencing delirium that prevented them from understanding that their action of committing a crime was wrong, they would qualify for this defense under the M'Naughten rule. This concept helps ensure that individuals who genuinely cannot comprehend their actions due to mental illness are treated differently from those who are fully aware of their behavior but choose to commit a crime.