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In the legal process, the insanity defenses are possible defenses by excuse, via which defendants may argue that they should not be held criminally liable for breaking the law, as they were mentally ill at the time of their allegedly criminal actions. It is important to note that the legal definition of "insane" in this context is quite different from the psychiatric definitions of "mentally ill". Also, the definition of insanity varies from one jurisdiction to another.

The insanity defense is still in use in the United States, while Australia and Canada have renamed it the mental disorder defence, and Commonwealth nations tend to shy away from it, partially due to the stigma of the word "insanity".

In England and Wales, for instance, the use of this defense is fairly rare. It is more common for someone with a mental illness to use the fact that they were mentally ill at the time of the offense as mitigation (which is distinct from a complete defense, which is what insanity is), or to use their mental state at the time of the trial to alter their sentence if found guilty (That is, once found guilty they receive an order committing them to a hospital rather than a prison sentence). When insanity is used, the person may still receive a hospital order.

The insanity defense is available in most jurisdictions that respect human rights and have a rule of law, though the extent to which it can or should be applied may differ widely between jurisdictions: for example, as in cases involving the battered-woman syndrome. Where the self-defense defense is not available, a defendant may be forced to choose between an insanity defense and provocation.

This defense is based on the principle that punishment is only reasonable if the defendant is capable of distinguishing right and wrong. A defendant making this argument might be said to be pleading "not guilty by reason of insanity"

See also Diminished responsibility.

Psychiatric treatments

Those found to have been not guilty by reason of insanity are generally then required to undergo psychiatric treatment; except in the case of temporary insanity (see below). Defendants found not guilty by reason of insanity are generally placed in a mental institution. Unlike defendants who are found guilty of a crime, they are not institutionalized for a fixed period, but rather they are held within the institution until authorities determine that they are no longer a threat. Authorities making this decision tend to be cautious; as a result, defendants can often spend more time there than they would have in prison (had they been convicted). In Foucha v. Louisiana (1992) the Supreme Court of the United States ruled that a person could not be held "indefinitely". People can be cured of insanity with the proper treatment.


In practice, a finding of "not guilty by reason of insanity" almost always requires that the defendant have been in a state of active psychosis (at the time the law was broken) and usually such findings involve a diagnosis of schizophrenia or schizoaffective disorder, but may even involve Bipolar disorder, particularly where the Bipolar disorder is accompanied by psychotic features. The use of the insanity defense in cases of psychopathy (antisocial personality disorder) is generally available only if the defendant has a co-occurring DSM-IV Axis I diagnosis, and then it becomes a difficult task for the forensic psychiatrist to determine whether the criminal act was the result of antisocial personality disorder or the Axis I diagnosis.

Incompetency, intoxication, and mental illness

An important distinction is the difference between competency and criminal responsibility. Competency deals with whether a defendant is able to adequately assist his attorney in preparing a defense, make knowing decisions concerning trial strategy and whether or not to plead guilty or accept a plea agreement. Criminal responsibility deals with whether a defendant can be held legally responsible for his criminal behavior. Thus, competency deals with the defendant's present condition, while criminal responsibility deals with the defendant's state of mind when he committed the crime.

In the United States, a trial in which the insanity defense is invoked typically involves the testimony of psychiatrists who will argue that the defendant is or is not insane. If there is agreement between the prosecution and defense that the defendant is insane then typically a jury trial is waived and a trial occurs in front of a judge in which evidence is presented and a judgment rendered. If there is disagreement between the prosecution and defense, each will typically present expert witnesses to a jury which will decide whose witnesses to believe.

The legal concept of insanity is different from the psychiatric concept of mental illness. Frequently, a person whose mental illness is not under dispute will be determined sane as the court will argue that despite a "mental illness" the defendant should still be held responsible; such a ruling is known as either a Guilty but Mentally Ill (GBMI) or a Guilty but Insane verdict. Michigan (1975) was the first state to create a GBMI verdict. Sometimes a person without mental illness can be found to be insane; for example, a person who is acting under the influence of a drug that was involuntarily administered (though voluntary intoxication has been rejected by most jurisdictions as a defense to crime). (See: Intoxication defense)

Controversy over the insanity defense

There are many different interpretations of "insane" and many different notions of how to deal with insane individuals.

Some opponents of the insanity defense, including Thomas Szasz, believe that psychiatry itself emerged as a way to justify mercy, of making persons "exceptional" and thus not deserving of the harsh punishment we would as a society wish to dole out to people who had extremely selfish or widely shared rationales for their actions. Since extreme selfishness ("self-absorption") or broadly shared resentments (e.g. envy of the rich, hatred of another ethnic group) are somewhat infectious behaviors, some argue that schizophrenia and other "mental illness" were defined into existence to protect those whose motives and behaviors were not so infectious, and whose offenses were thus unlikely to be repeated by others. The cost of this system of mercy, however, was to classify the psychiatrist and patient in an ongoing unequal-power relationship. (See myth of mental illness and antipsychiatry).

The public tends to believe that the insanity defense is used more often than it actually is, possibly because insanity defense cases tend to be of a high-profile nature. The insanity plea is used in the U.S Criminal Justice System in less than 1% of all criminal cases, and only one fourth of those defendants are found "not guilty by reason of insanity".

Some U.S. courts have begun to ban the use of the insanity defense and a 1994 Supreme Court ruling upheld the right of Montana to do so. Idaho and Utah have also banned this defense. In 2006, the Supreme Court decided Clark v. Arizona, reaffirming the prerogative of the states to deviate from or even totally abolish the insanity defense.

One novel use of the insanity defense occurred in the case of Lee Boyd Malvo, who plead not guilty by reason of insanity in the autumn 2003 Beltway sniper shootings. Many legal experts believe [How to reference and link to summary or text] that the purpose of raising the defense was not to gain an acquittal but to allow the defense to introduce otherwise inadmissible evidence about Malvo's upbringing, his relationship with John Allen Muhammad, and his mental state. This evidence was intended to gain the jury's sympathy so that they would not invoke the death penalty, and was successful at doing so.

Rules of appreciation

In this section, various rules applied in United States jurisdiction with respect to insanity defences are discussed.

The M'Naghten Rules

The M'Naghten Rules (1843) 10 C & F 200, state, inter alia, that a person may be "insane" if " the time of the committing of the act, the party accused was labouring under such a defect of reason, arising from a 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 what he was doing was wrong." These rules are, as of 2006, in force in the majority of common law jurisdictions.

The irresistible impulse

There is also an idea of an irresistible impulse, which argues that a person may have known an act was illegal; but, because of a mental impairment, they couldn't control their actions. In 1994, Lorena Bobbitt was found not guilty of the felony of "malicious wounding" (the equivalent of mayhem), when her defence argued that an irresistible impulse led her to cut off her husband's penis. In the late nineteenth century some states and federal courts in the United States, dissatisfied with the McNaughten rule, adopted the irresistible impulse test. This test, which had first been used in Ohio in 1834, emphasized the inability to control one's actions. A person who committed a crime during an uncontrollable "fit of passion" was considered insane and not guility under this test.

The Durham rule

The Durham Rule or "product test" was set forth by the United States Court of Appeals for the District of Columbia Circuit in 1954 and states that "... an accused is not criminally responsible if his unlawful act was the product of mental disease or defect". After the 1970s, US jurisdictions have tended to not recognize this argument as it places emphasis on "mental disease or defect" and thus on testimony by psychiatrists and is argued to be somewhat ambiguous.

The Brawner rule

The Brawner Rule (The United States v. Brawner, 1972) by the District of Columbia Appeals set aside the Durham ruling arguing the ruling’s requirement that a crime must be a “product of mental disease or defect” placed the question guilt on expert witnesses and diminished the jury’s role in determining guilt. Under this proposal, juries are allowed to decide the "insanity question" as they see fit. Basing its ruling on the American Law Institute’s (ALI) Model Penal code, the court ruled that for a defendant to not be criminally guilty for a crime the defendant, “(i) lacks substantial capacity to appreciate that his conduct is wrongful, or (ii) lacks substantial capacity to conform his conduct to the law.”

It is noteworthy that this case was (1) decided by the District of Columbia District Court of Appeals and not the United States Supreme Court, and is thus not a national precedent, and (2) not based on constitutional arguments and was thus superseded by Congress in 1984 with The Insanity Defense Reform Act of 1984.

The Insanity Defense Reform Act of 1984 (U.S.)

There was widespread public outcry over John Hinckley Jr.'s successful use of the insanity defense in his trial for the attempted assassination of Ronald Reagan. The Insanity Defense Reform Act of 1984, enacted by Congress in 1984 in response to the verdict in the Hinckley trial, and codified at Title 18, U.S. Code, Section 17, states that a person accused of a crime can be judged not guilty by reason of insanity if "the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts."

The Insanity Defense Reform Act is also notable because of its shift of the burden of proof from the prosecution proving a defendant sane declaring, “The Defendant has the burden of proving the defense of insanity by clear and convincing evidence.”

The substantial capacity test

The substantial capacity test was defined by the American Law Institute, in its Model Penal Code. This argues that insanity should be defined as a lack of substantial capacity to control one's behavior. Substantial capacity is defined as: "the mental capacity needed to understand the wrongfulness of [an] act, or to conform...behavior to" This is related to the M'Naghten Rule and the idea of 'irresistible impulse'.

Temporary insanity

The notion of temporary insanity argues that a defendant was insane, but is now sane. A defendant found to have been temporarily insane will often be released without any requirements of psychiatric treatment. This defense was first used by U.S. Congressman Daniel Sickles of New York in 1859 after he had killed his wife's lover, Philip Barton Key, but was most used during the 1940s and 1950s. Since then, it has not been as successful.

Scottish law

The Scottish Law Commission in its Discussion Paper No 122 on Insanity and Diminished Responsibility (2003) [1] pp.16/18 confirms that the law has not substantially changed from the position stated in Hume's Commentaries:

We may next attend to the case of those unfortunate persons, who have plead the miserable defence of idiocy or insanity. Which condition, if it is not an assumed or imperfect, but a genuine and thorough insanity, and is proved by the testimony of intelligent witnesses, makes the act like that of an infant, and equally bestows the privilege of an entire exemption from any manner of pain; Cum alterum innocentia concilii tuetur, alterum fati infelicitas excusat. I say, where the insanity is absolute, and is duly proved: For if reason and humanity enforce the plea in these circumstances, it is no less necessary to observe a caution and reserve in applying the law, as shall hinder it from being understood, that there is any privilege in a case of mere weakness of intellect, or a strange and moody humour, or a crazy and capricious or irritable temper. In none of these situations does or can the law excuse the offender. Because such constitutions are not exclusive of a competent understanding of the true state of the circumstances in which the deed is done, nor of the subsistence of some steady and evil passion, grounded in those circumstances, and directed to a certain object. To serve the purpose of a defence in law, the disorder must therefore amount to an absolute alienation of reason, ut continua mentis alienatione, omni intellectu careat - such a disease as deprives the patient of the knowledge of the true aspect and position of things about him - hinders him from distinguishing friend from foe - and gives him up to the impulse of his own distempered fancy.

The phrase "absolute alienation of reason" is still regarded as at the core of the defence in the modern law (see HM Advocate v Kidd 1960 JC 61 and Brennan v HM Advocate (1977) JC 38).

Insanity Defense Origins

According to Mark Gado, a writer for Court TV’s Crime Library, the insanity defense has developed from centuries of legal standards. The legal definition for insanity continued to adjust as new events took place. However, it did not become an official defense until the 1843 case of Daniel M’Naughten.

Daniel M’Naughten (many spelling variations but "McNaughton" is on original court and hospital documents) was a woodturner from Scotland. He became convinced, for whatever reason, that there was a conspiracy to kill him. He shot and killed Edward Drummond, Prime Minister Robert Peel’s secretary, when he was in London thinking he was one of a crew that had been following him. M’Naughten’s lawyers argued in court that he was insane - using all variations of insanity argument and expert testimonly by the defense was not rebutted by the Crown. A jury acquitted him of the murder charge by reason of insanity but McNaughton spent the remainder of his life incarcerated in a mental facility.

The British House of Lords released a ruling based on M’Naughten’s case that stated the definition of the insanity defense. The ruling, which became known as the M’Naughten Rules, became the general guidelines by which the insanity defense was judged for decades in most common law and even some civil law countries.

Determining Legal Insanity

Insanity is purely legal in definition when it relates to its usage as a defense. Frank Schmalleger, author of Criminology Today, wrote that there are several tests that exist today that are used to measure whether or not a criminal is insane.

The M’Naughten Rule was one of the first insanity tests and is still widely used today. It states that a person can not be guilty of a crime, if at the time they committed it they were unaware of what they did or did not realize that it was wrong.

A unique argument for the insanity defense is the issue of irresistible-impulse. This prompted the irresistible-impulse test which states that a person is insane if their mind prevented them from resisting the urge to commit the crime that they are charged with. Schmalleger says that this test is used by only eighteen states.

The 1954 Monte Durham brought about another insanity test. The Durham Rule says that someone accused of a crime can not be convicted if that crime was the result of a mental disease or defect that they possess. It does not state what the difference between a mental disease and a defect is though, so it is difficult to know which definition a particular offender falls into.

A rule that is completely different from all of the other insanity tests is the Brawner Rule. The 1972 United States vs. Brawner case allows the jurors to be the people who decide whether or not the defendant is insane. They have to decide if a defendant could be fairly convicted of the crime they are accused of doing. Because juries have virtual free reign in defining insanity, this rule has not been used very much.

The fact that mentally unstable people weren’t being sentenced properly and that people were falsely using the insanity defense prompted many states to create a new verdict, guilty but mentally ill (GBMI). The GBMI allows for a mentally unstable person to be convicted of a crime. Judges are allowed to give any sentence to defendants who receive a verdict of GBMI, but offenders are usually sent to hospitals where they can get help for their illness.

Insanity Defense Usage and Success Rate

Media coverage in the United States tends to dictate how situations are perceived by the public. A case using the insanity defense usually receives a lot more media attention because it is such a strange defense strategy. The increased media coverage gives the impression that the insanity defense is used a lot, but this is not the case. According to A Crime of Insanity: Insanity on Trial, an insanity article on the PBS Web Site, the insanity defense is used in less than one percent of felony cases. Only a small fraction of those cases that claim that the defendant is insane actually succeed.

Famous Insanity Defense Cases

Like any other issue in the news, big cases involving the insanity defense are the ones that receive the most media coverage and are kept alive the longest by the public. Two of the more recent famous cases that employed the insanity defense were those of Lee Boyd Malvo and Andrea Yates.

Lee Boyd Malvo, along with John Allen Muhammad, was responsible for the murders of ten people in 2002. He was nicknamed “D.C. Sniper” because the killings took place near Washington D.C. An article written by a CNN correspondent said that when Malvo went on trial for the October shooting of Linda Franklin, one of the ten people murdered, he pleaded not guilty by reason of insanity. His lawyers tried to prove that Malvo had been corrupted by Muhammad and could not be held responsible for what happened. A jury didn’t buy this defense and found him guilty of the murder on December 18th 2003.

Andrea Yates was successful in her use of the insanity plea. According to Richard Vatz in his article Murderous Mothers, Andrea Yates was put on trial for the drowning of her five children. Her legal defense attempted to prove that she was insane when she committed the murders. A jury decided that she was mentally stable and thus able to stand trial for the murders. She was convicted and sentenced to life in prison. However, that sentence was overturned when she won on appeal that there was error in her Dr's testimony. She won her second trial and was sentenced to Not Guilty By Reason of Insanity. She cannot be tried again, on her other two sons murders. She may one day be free, if she is found to be recovered. She is In Hospital in the State of TX.

Angie Cannon said it best in Sniper Insanity when she wrote, “Insanity defenses are usually an uphill battle. Juries often don’t buy the idea that someone can’t distinguish right from wrong.” It is extremely hard to prove that someone is indeed insane. It seems that the bigger the crime is and the more media coverage it gets is consistent with the success or failure of the insanity plea. The higher up an insanity case is on the criminal food chain generally means that it will not be successful.

See also


  • Bienstock, Mothers Who Kill Their Children and Postpartum Psychosis, (2003) Vol. 32, No. 3 Southwestern University Law Review, 451.
  • Dalby, J,T. The Case of Daniel McNaughton: Let's Get the Story Straight (2006) American Journal of Forensic Psychiatry, 27, 17-32.
  • Dressler, Joshua, Reaffirming the Moral Legitimacy of the Doctrine of Diminished Capacity: A Brief Reply to Professor Morse, (1984) Vol. 75 Journal of Criminal Law & Criminology, 953.
  • Gorr, Michael J., and Harwood, Sterling, eds., Controversies in Criminal Law: Philosophical Essays on Responsibility and Procedure (Boulder, CO: Westview Press, 1992), 273pp.
  • Keram, The Insanity Defence and Game Theory: Reflections on Texas v. Yates, (2002) Vol. 30, No. 4 Journal of the American Academy of Psychiatry and the Law, 470.
  • Koppel, Ted, et al., "Is Abuse an Excuse?," in Michael J. Gorr and Sterling Harwood, eds., Crime and Punishment: Philosophic Explorations (Belmont, CA: Wadsworth Publishing Co., 2000, formerly Boston, MA: Jones and Bartlett Publsihers, 1996), pp. 529-549.
  • Moore, Michael S., "Legal Conceptions of Mental Illness," in Michael J. Gorr and Sterling Harwood, eds., Controversies in Criminal Law: Philosophical Essays on Responsibility and Procedure (Boulder, CO: Westview Press, 1992), pp. 125-162.
  • Rosen, Cathryn Jo, "The Battered Woman's Defense," in Michael J. Gorr and Sterling Harwood, eds., Controversies in Criminal Law: Philosophical Essays on Responsibility and Procedure (Boulder, CO: Westview Press, 1992), pp. 89-99.
  • Schopp, Robert F. (1991) Automatism, Insanity, and the Psychology of Criminal Responsibility, Cambridge: Cambridge University Press, ISBN 0-521-40150-X.
  • Schopp, Robert F. (2001) Competence, Condemnation, and Commitment: An Integrated Theory of Mental Health Law, American Psychological Assn., ISBN 1-55798-745-9.
  • Slobogin, An End to Insanity: Recasting the Role of Mental Disability in Criminal Cases, (2000) Vol. 86 Virginia Law Review, 1199.
  • Taylor, Lawrence and Dalton, Katharina, "Premenstrual Syndrome: A New Criminal Defense?,", in Michael J. Gorr and Sterling Harwood, eds., Controversies in Criminal Law: Philosophical Essays on Responsibility and Procedure (Boulder, CO: Westview Press, 1992), pp. 163-179.
  • “A Crime of Insanity: Insanity Defense FAQs.” Public Broadcasting System.
  • Cannon, Angie. “Sniper Insanity?” U.S. News & World Report 135 (2003).
  • Gado, Mark. “All about the insanity defense.” Courtroom Television Network.
  • Leighton, Paul. “Insanity Defense.” 2005.
  • Schmalleger, Frank. Criminology Today: An Integrative Introduction. Fourth Edition. New Jersey: Person Prentice Hall, 2004.

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