Legal Definition of Insanity

In a court case where the insanity defense is being considered, it is important to clarify where the term "insanity"  is defined.  It is a legal definition and not a definition given by the medical community.   If a person pleads insanity, the jury decides whether that person’s criminal act will be excused or they will be held responsible. Psychiatrists do not determine whether a person is insane.

Listed below are a number of rules and test used within the criminal justice system for determining the sanity of a defendant.
 

M'Naghten Rule

The insanity defense dates back to 1843, when Daniel M’Naghten was acquitted for attempting to assassinate British Prime Minister Sir Robert Peel. Later that same year, the House of Lords issued the following ruling:

“To establish a defense on the ground of insanity, it must clearly be proved that, at the time of the committing of the act, the party accused was laboring 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 was wrong”

This ruling became know as the M’Naghten Rule and for over a century, has been the standard for the insanity defense. To meet the standard set for by M'Naghten, a person must acting under a delusion so overpowering that  he is incapable of appreciating and understanding his surroundings.

The Irresistible Impulse Test

A person with mental disease is excluded from criminal responsibility when the disease makes it impossible to control personal conduct. Unlike the M'Naghten Rule, the criminal may be able to distinguish between right and wrong.  However, he is unable to exercise self-control because of a disabling mental condition.

The Durham Rule (Products Test)

This rule is based on the thought that insanity represents many personality factors, all of which may not be present in every case. Judge David Bazelon made this ruling in the case of Durham v. U.S. when he rejected the M'Naghten Rule and stated that the accused is not criminally responsible if the unlawful act was the result of a product of mental disease or defect.

The Substantial Capacity Test

The focus of the test is on the reason and will of the accused. It states that at the time of the crime, and as a result of some mental disease or defect, the defendant lacked the substantial capacity to appreciate the wrongfulness of his conduct or was unable to conform his conduct to the requirements of the law.

According to Barry Wall,
Clinical Assistant Professor of Psychiatry at Brown University

"The insanity defense itself is much maligned and misunderstood. The public often believes that insanity pleas are commonly used, particularly by the rich, to "fake" illness to elude punishment, and that it’s wildly successful. The opposite is true: It is used in less than 1 percent of cases, it fails 75 percent of the time, and it’s rarely used by fakers. If you’re found to be insane, in many states you actually risk spending more time locked up in a mental hospital than you would if you’d been found guilty and served jail time."

Mental Illness  ‌  Legal Definition  ‌  Justice Issues  ‌  Statistics
 Case Studies   ‌  Celebrities   ‌   Organizations
Contact Us!   ‌   Home

Copyright © 2003-2007
Questions, comments or suggestions for this website are most welcome.
Last modified: April 8, 2007.