The
insanity defense, also known as the
mental disorder defense, is a
defense by
excuse in criminal trials arguing that the defendant is not responsible for their actions due to an episodic or persistent
psychiatric illness. Exemption from full criminal punishment on such grounds dates back to at least the
Code of Hammurabi. Legal definitions of insanity or mental disorder are varied, and include the
M'Naghten Rules, the
Durham rule, the American Legal Institute definition, and other provisions, often relating to a lack of
mens rea ("guilty mind"). In the
criminal laws of Australia and Canada, statutory legislation enshrines the
M'Naghten Rules, with the terms
defence of mental disorder,
defence of mental illness or
not criminally responsible by reason of mental disorder employed.