Mental Disease or Defect

Fundamentals of Criminal Law by Adam J. McKee

Although widely unpopular, most states and the federal government recognize some sort of insanity defense (e.g., 18 U.S.C. § 17). The term insanity comes from the law; psychology and medicine do not use it. The everyday use of the term can be misleading.

If a person acts abnormally, they tend to be considered by many as “crazy” or “insane.” At law, merely having a mental disease or mental defect is not adequate to mitigate guilt. Jeffrey Dahmer, for instance, was determined to be legally sane, even though he was seriously mentally ill.

The Rationale Behind the Insanity Defense

The logic of the insanity defense goes back to the idea of mens rea and culpability. Society generally wishes to punish those who understood the wrongfulness of their actions. It is seen as morally wrong to punish someone for an unavoidable accident or very young children for acts that would be deemed criminal if committed by adults. If a person lacks the understanding that their action is wrong due to their mental condition, it’s deemed morally wrong to punish them.

Different Tests for Legal Insanity

The concept of legal insanity, while seemingly straightforward, is layered with complexities and has been the subject of considerable debate within the legal system. As societies evolve and our understanding of mental health deepens, so too has the approach to determining legal insanity. Historically, courts have grappled with how to measure it in a manner that is both fair and reflective of current medical and psychological understanding. To systematically evaluate if a criminal defendant is legally insane, different jurisdictions have developed specific tests over the years.

Each test is structured to encapsulate the intricacies of mental health conditions and their impact on individuals’ ability to discern right from wrong or control their actions. These tests not only aim to ascertain the defendant’s mental state at the time of the crime but also to ensure that justice is meted out in a manner that recognizes the nuances of human psychology and behavior. The diversity in these tests across jurisdictions underscores the challenges inherent in balancing legal principles, societal expectations, and medical insights in the realm of criminal responsibility.

The M’Naghten Rule

Originating in the mid-19th century, the M’Naghten rule stands as one of the foundational benchmarks for evaluating legal insanity within the criminal justice system. Born out of the infamous 1843 case involving Daniel M’Naghten, a man who mistakenly assassinated a secretary in the belief that he was targeting the British Prime Minister, this rule was established as a response to the ensuing public outcry when M’Naghten was found not guilty by reason of insanity. The central tenet of the M’Naghten rule pivots on an individual’s cognitive capability: specifically, whether the defendant, due to a mental defect, was unable to comprehend the nature of the act they were committing or failed to recognize that the act was wrong.

In application, the M’Naghten rule places a lens on the defendant’s mental state during the commission of the crime. For the defense to succeed, it must be demonstrated that the individual was so deeply enshrouded in their delusions or mental afflictions that discerning right from wrong became an insurmountable challenge. As such, the rule doesn’t merely recognize the existence of a mental disorder but delves deeper, seeking to understand how that disorder affected the person’s moral and cognitive faculties. Over time, while many jurisdictions have developed and adopted more comprehensive standards for legal insanity, the M’Naghten rule’s emphasis on moral cognition remains an influential touchstone in discussions surrounding criminal responsibility and mental health.

The Irresistible Impulse Test

In the annals of legal history, the Irresistible Impulse Test emerges as a significant development in our understanding of criminal culpability in the context of mental illness. First adopted by the Alabama Supreme Court in the landmark case of Parsons v. State in 1887, this test brought forth a nuanced perspective on the intricate interplay between mental disorders and one’s ability to regulate their actions. While earlier benchmarks, like the M’Naghten rule, focused primarily on cognitive recognition of right and wrong, the Irresistible Impulse Test delved into the realm of uncontrollable actions driven by severe mental disturbances.

At its core, the test seeks to address a poignant question: Can an individual be held fully accountable for an act they fundamentally couldn’t resist due to the overwhelming force of their mental condition? It acknowledges the profound grip certain mental illnesses can exert on a person, to the extent that, despite a clear understanding of the wrongful nature of an act, they find themselves compelled to act without restraint. This paradigm shift broadened the scope of legal defenses, recognizing that mental illness doesn’t solely distort cognitive recognition but can also severely hamper an individual’s willpower and self-control. The adoption of the Irresistible Impulse Test represented a deeper, more comprehensive exploration of the challenges faced by individuals with mental disorders within the criminal justice system, emphasizing the complexities of human behavior and the profound impacts of mental health on decision-making.

The Substantial Capacity Test

In an effort to harmonize and modernize the varied standards surrounding the insanity defense, the Model Penal Code (MPC) introduced the Substantial Capacity Test, which has since been embraced by the majority of federal and state courts in the United States. As outlined in Section 4.01 of the MPC, the Substantial Capacity Test establishes that a person should not be held criminally responsible for their actions “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.”

This test effectively marries two central tenets from its historical predecessors. Firstly, it integrates the cognitive element from the M’Naghten rule, which emphasizes a defendant’s ability (or lack thereof) to appreciate or understand the wrongfulness of their actions. Secondly, it embodies the core principle of the Irresistible Impulse Test by considering whether the defendant, due to their mental disease or defect, was unable to control their actions in accordance with the law.

By combining these standards, the Substantial Capacity Test acknowledges the multifaceted nature of mental illness, recognizing that it can impair both an individual’s cognitive understanding of their actions and their ability to control those actions. As such, it offers a more holistic and comprehensive approach to evaluating criminal culpability in the context of mental health, ensuring that the nuances and complexities of such cases are adequately addressed in the courts.

Hollywood Myths vs. Reality

Contrary to popular belief fueled by Hollywood, the insanity defense is rarely used by defendants and is even less often successful. Most individuals who successfully employ it end up spending more time in mental institutions than they would in prison if convicted. It’s a misconception to view the insanity defense as a “get out of jail free card.”

Modification History

File Created:  07/17/2018

Last Modified:  09/26/2023

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This work is licensed under an Open Educational Resource-Quality Master Source (OER-QMS) License.

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