Omar Bennett
The insanity defense has been a highly debated topic among lawyers and the public for decades, with the definition of insanity varying across different jurisdictions. In the US, the insanity defense is determined by the M'Naghten Rule in 21 states, the Model Penal Code in 16 states, an adaptation of the Model Penal Code in 8 states, and 6 states have abolished the defense altogether. The M'Naghten Rule, based on the case of Daniel M'Naghten in 1843, focuses on the defendant's ability to understand right from wrong and their intellectual capacity. The Model Penal Code, on the other hand, considers both rationality and lack of control. The insanity defense is further complicated by the differing philosophies of psychiatrists, psychologists, and legal professionals, as well as the role of judges, juries, and medical experts. While the defense of insanity has been recognized since 1581, its application and definition continue to evolve, with recent cases such as Kahler v. Kansas impacting the legal landscape.
| Characteristics | Values |
|---|---|
| Test for insanity | M'Naghten Rule, Irresistible Impulse test, Durham Rule, Model Penal Code test, McNaughten's rule, Substantial capacity test |
| Basis of test | Whether the accused knew the nature of the crime, or could distinguish right from wrong |
| Burden of proof | Defendant must prove insanity by "clear and convincing evidence" |
| Understanding of right and wrong | Intellectual understanding of right and wrong, rather than a moral or affective definition |
| Lack of control | Not considered a valid defense in some jurisdictions |
| Competency | Whether a defendant is able to adequately assist their attorney in preparing a defense |
| Criminal responsibility | Whether the defendant is responsible for their actions as a result of their mental disease or defect |
| Mental impairment | The accused was suffering from a mental impairment that affected their ability to understand the nature and quality of their actions |
| Legal vs. medical insanity | Only legal insanity (mental illness at the time of committing the crime) falls within the purview of insanity laws |
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What You'll Learn
The M'Naghten Rule
The rule states that:
> Every man is to be presumed to be sane, and … that to establish a defence 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 mind, and 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.
In other words, a defendant must meet one of these two distinct criteria for a court to declare them legally insane: either they did not know the nature and quality of their actions, or they did know but did not know it was wrong. This is also known as the "test of knowing" or the "test of right and wrong".
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The Irresistible Impulse Test
In jurisdictions where it is recognised as an affirmative defence, defendants seeking to prove irresistible impulse are generally required to demonstrate two key elements: the existence of mental illness, and the causation of the inability to control actions. This requires proof of a causal link between the diagnosed mental illness and the defendant's incapacity to control their actions, showing how the mental illness directly contributed to their inability to exercise control.
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The Durham Rule
As a result of these criticisms and concerns, federal and most state courts in the United States abandoned the Durham Rule in 1972. Today, New Hampshire is the only state that still uses this rule, but it has narrowed its interpretation to apply only to the most serious cases.
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The Model Penal Code Test
The test asks whether, at the time of committing the crime, the defendant, as a result of a severe mental disease or defect, lacked substantial capacity either to appreciate the criminality of their conduct or to conform their conduct to the requirements of the law. This is a broader test than the M'Naghten Rules, which are based on the understanding of right and wrong. The Model Penal Code Test allows for a more flexible interpretation of insanity, as it does not require a total lack of capacity but rather a substantial one.
The test also allows for a choice between the language of "criminality" and "wrongfulness". This allows for a more nuanced understanding of the defendant's mental state, as it can take into account whether the defendant knew their actions were morally wrong, not just legally wrong.
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The Substantial Capacity Test
> "A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality [wrongfulness] of his conduct or to conform his conduct to the requirements of law."
The test was first used in 1982, when John Hinckley successfully pleaded insanity in his federal trial for the attempted murder of then-President Ronald Reagan. The test differs from the M'Naghten standard in that it uses the word \"appreciate\" rather than \"know\". "Appreciate" incorporates an emotional quality, which means that evidence of the defendant's character or personality is relevant and most likely admissible to support the defence.
The test also differs from the M'Naghten standard in terms of the burden of proof. Under the M'Naghten standard, the defendant must prove their insanity, whereas under the Substantial Capacity Test, the burden shifts back to the state to prove beyond a reasonable doubt that the defendant was not insane at the time of the crime.
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Frequently asked questions
The insanity defense is a legal argument that a defendant is not responsible for a crime due to mental illness or insanity.
Different jurisdictions have adopted different standards to determine whether an accused person is legally insane. These include the M'Naghten Rule, the Irresistible Impulse test, the Durham Rule, and the Model Penal Code test.
The M'Naghten Rule, also known as the "right and wrong" test, seeks to determine whether the accused person knew the nature of the crime they are alleged to have committed and could distinguish right from wrong at the time it was committed. This is the most widely used test for criminal insanity in the United States.
The Irresistible Impulse test broadened the scope of the M'Naghten Rule by considering not just whether the accused person could distinguish right from wrong, but also whether they could control their impulse to commit the wrongful act.
