Criminal insanity is a form of personal defense. It is important to understand that legal definitions of criminal insanity often have very little to do with psychological or psychiatric understandings of mental illness. Legal criminal insanity is a concept developed over time to meet the needs of the judicial system in assigning guilt or innocence to particular defendants. It is not primarily concerned with treatment, as is the idea of mental illness in psychiatry. Medical conceptions of mental illness do not always fit well into the legal categories created to deal with the phenomenon. This difference has led to a situation in which mental health professionals often appear to give contradictory testimony in criminal trials.


The McNaughten Rule

: Prior to the nineteenth century the criminal insanity defense was nonexistent. Insane people who committed crimes were punished in the same way as other law violators. It was Daniel McNaughten, also spelled M'Nagheten, a woodworker from Glasgow, Scotland, who in 1844, become the first person to be found not guilty of a crime by reason of criminal insanity. McNaughten had tried to assassinate Sir Robert Peel, the British prime minister. He mistook Edward Drummond, Peel's secretary, for Peel himself, and killed Drummond instead. At his trial, defense attorneys argued the McNaughten suffered from vague delusions centered on the idea that the Tories, a British political party, were persecuting him. Medical testimony at the trial agreed with the assertion of McNaughten's lawyers that he didn't know what he was doing at the time of the shooting. The judge accepted McNaughten's claim, and the criminal insanity defense was born. The McNaughten rule, as it has come to be known, was defined later by the courts and still plays a major role in determining insanity in criminal prosecutions in fifteen states today.

The McNaugten rule holds that a person is not guilty of a crime if, at the time of the crime, they either didn't know what they were doing, or didn't know that what they were doing was wrong. The inability to distinguish right from wrong must be the result of some kind of mental defect or disability. Note that it the burden of proving insanity falls upon the defendant.

Irresistible Impulse

: The McNaugten rule worked for a time, but eventually, some cases arose in which defendants clearly knew what they were doing, and they knew it was wrong. They instead argued in their defense, that they couldn't help themselves. They couldn't stop doing that which was wrong. These people are said to suffer from an irresistible impulses and may be found not guilty by reason of that particular brand of insanity in eighteen of the United States. Some states which do not use the irresistible impulse test in determining criminal insanity may still allow the successful demonstration of such an impulse to be considered in sentencing decisions.

The Durham Rule:

A third rule for gauging criminal insanity is called the Durham rule. It was created in 1871 by a New Hampshire court and later adopted by Judge David Bazelon in 1954 when he sat on the bench for the case of Durham v. United States in the Court of Appeals in the District of Columbia. The Durham Rule states that a person in not criminally responsible for their behavior if their illegal actions were the result of some mental disease or defect.

Courts which follow the Durham rule will typically hear from an a group of psychiatric specialists as to the mental state of the defendant. A successful defense under the Durham rule necessitates that jurors be able to see the criminal activity in question as the "product," of mental deficiencies harbored by the defendant.

The Substantial Capacity Test

: Nineteen stated follow the Substantial Capacity Test, as found in the Model Penal Code of the American Law Institute. Also called the ALI rule or the MPC rule, it suggest that criminal insanity should be defined as the lack of substantial capacity to control one's behavior. The test requires a judgment to the effect that the defendant either had or lacked, "the mental capacity needed to understand the wrongfulness of his act, or to conform his behavior to the requirements of the law." This rule is a blending of the McNaughten rule with the irresistible impulse standard. "Substantial Capacity," does not require total mental incompetence nor does the rule require the behavior in question to live up to the criteria of total irresistibility.

The Brawner Rule

: Judge Bazelon, dissatisfied with the application of the Durham rule, created a new criteria for gauging criminal insanity in the 1972 case of U.S. v. Brawner. The Brawner rule, as it has come to be known, places responsibility for deciding criminal insanity squarely wit the jury. Bazelon suggested that the jury should be concerned with whether or not the defendant could be justly held responsible for the criminal act in the face of any claims of criminal insanity.

Guilty but Insane

: A newer finding of guilty but insane (in a few states the finding is guilty but mentally ill, or GBMI) is now possible in some jurisdictions. It is one form the response to public frustration with the criminal insanity issue has taken. Guilty but insane means that a person can be held responsible for a specific criminal act, even though a degree of mental incompetence may be present in his or her personality. Upon return of this verdict, a judge may impose any sentence possible under the law for the crime in question. However, mandated psychiatric treatment will generally be part of the commitment order. The offender, once cured, will be placed in the general prison population to serve any remaining sentence. In 1975 Michigan became the first state to pass a "guilty but mentally ill" statute, permitting a GBMI finding.

Temporary Insanity

: Temporary insanity is another possible defense against a criminal charge. Widely used in the 1940s and 1950s, temporary insanity meant that the offender claimed to be criminally insane only at the time of the commission of the offense. If a jury agreed the defendant virtually went free. The suspect was not guilty of the criminal action by virtue of having been criminally insane and could not be ordered to undergo psychiatric counseling or treatment because the insanity was no longer present. This type of plea has become less popular as legislatures have regulated the circumstances under which it could be made.

The Insanity Defense Under Federal Law:

In 1984 the U.S. Congress passed the federal Insanity Defense Reform Act. The act created major revisions in the federal insanity defense. Criminal insanity under the law is now defined as a condition in which the defendant can be shown to have been suffering under a "severe mental disease or defect" and as a result, "was unable to appreciate the nature and quality or the wrongfulness of his acts." This definition of criminal insanity comes close to that set forth in the old McNaughten rule.


The criminal insanity defense originated as a means of recognizing the social reality or mental disease. Unfortunately, the history of this defense has been rife with change, contradiction, and uncertainty. Psychiatric testimony is expensive, sometimes costing thousand of dollars per day for one medical specialist. Still worse is the fact that each "expert" is commonly contradicted by another.

Public dissatisfaction with the jumble of rules defining legal insanity peaked in 1982, when John Hinckly was acquitted of trying to assassinate President Reagan. At his trial Hinckly's lawyers claimed that a series of delusions brought about by a history of schizophrenia left him unable to control his behavior. Government prosecutors were unable to counter the defenses contentions of insanity. The resulting acquittal shocked the nation and resulted in calls for a review of the insanity defense.

The insanity defense today is not an "easy way out," of criminal prosecution, as some have assumed. One a verdict of "not guilty by reason of criminal insanity" is returned, the judge may order the defendant to undergo psychiatric treatment until cured. Due to the fact that psychiatrists are reluctant to declare any potential criminal cured, such a sentence may result in more time spent in an institution that would have resulted from a prison sentence. Of an interesting note, the states of Idaho and Kansas have abolished the insanity defense. The states of Montana and Utah have abolished the insanity defense but have allowed guilty but mentally ill verdicts.