A more thorough explanation:

McNaghten rules refer to a legal doctrine in criminal law that states a person cannot be held criminally responsible for an act if they had a mental disability that prevented them from knowing the nature and quality of the act or whether it was right or wrong.

For example, if a person with a mental illness commits a crime but did not understand the consequences of their actions, they may be found not guilty by reason of insanity under the McNaghten rules.

The McNaghten rules have been adopted by federal courts and most states in some form and are also known as the right-and-wrong test or the right-wrong test.

It is important to note that the McNaghten rules only apply in cases where there is a "defect of reason, from disease of the mind." If a person knew what they were doing and knew it was wrong, they cannot use the McNaghten rules as a defense.