The M’Naghten Rule

By Stephanie Lee

Prior to the M’Naghten Rules being in place the “insane” were not held responsible for their actions.  Ancient Hebrew laws stated that “idiots, lunatics, and children” are unable to tell the difference between good and evil thus relieving them of responsibility for their actions (Maeder, 1985).

However, starting with the 13th century in England, more cases dealing with the “insane” were being dealt with.  The test for whether or not these people were “insane” was really up to whoever was king at the time.  Over time it shifted to looking at the person on trial and then other people would use their human judgement to determine whether or not they were able to tell good from evil (Weinreb, 1986).

Daniel M'Naghten

This all came to a screeching halt in 1843 when the public was outraged that Daniel M’Naghten was acquitted of his charges for his attempted assassination of the Prime Minister (accidentally shooting the Secretary to the Prime Minister who he mistook for the Prime Minister of England at the time, Robert Peel) because he was deemed “insane” and thus void of responsibility of his own actions (Weinreb, 1986).   Due to the outcry of the Queen and the public, the House of the Lord posed questions for the Central Criminal Court regarding what “insanity” was.  One of the judges answersed:

“in all cases that every man is to be presumed to be sane…until the contrary be proved…and that to establish a defense on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or if he did know it, that he did not know he was doing what was wrong” (The Daniel M’Naghten’s Case, 1843, p. 722)

This very answer was what became the M’Naghten rule (Garrison, 1998).

This rule was adopted and used in the United States court system by 1851.  However, there were very many criticisms about this rule both in the United States and back in England.  This rule did three things that made it critically insufficient as an insanity test:

  1. the rule is not in accord with psychiatric knowledge
  2. the rule does not permit complete and adequate testimony
  3. the psychiatric expert testifying under the rule does not make a scientific contribution but assumes the role of ethical judge

Do to this, and other circumstances, the rule in America would be deemed for change (Slovenko, 1994).


Garrison, A. H. (1998). The history of the M’Naghten insanity defense and the use of posttraumatic stress disorder as a basis of insanity. American Journal of Forensic Psychology, 16, 39-88.

Maeder, T (1985). Crime and madness: The origins and evolution of the insanity defense. Harper and Row Publishers

National Environmental Policy Act of 1969 § 102, 42 U.S.C. § 4332 (1994).

Slovenko, R. (1994). Psychiatry and criminal sulpability. John Wiley and Sons, Inc.

The Daniel M’Naghten’s Case 1843 10 Cl. & F. 200, § 847, 8 U.S.C. Rep. 718 (1843)

Weinreb, L. (1986). Criminal law, 4th edition. University Casebook Series, Inc.

Comments are closed.