Psychology The Insanity Defense
Michael J. Vitacco
  • LAST REVIEWED: 25 July 2023
  • LAST MODIFIED: 25 July 2023
  • DOI: 10.1093/obo/9780199828340-0318


The insanity defense is a legal standard that deals with determining culpability for criminal acts. When met, it absolves the individual of a criminal act they committed, although they are typically mandated to a secure hospital for treatment. As defined in federal jurisdictions under 18 U.S.C. §17(a), insanity “is an affirmative defense under any Federal Statute that, at the time of the commission of the acts constituting the offense, the defendant as a result of severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts.” The presence of a mental disease or defect is considered a threshold condition, meaning it first must be determined if a mental disease or defect exists, and then determined if that condition was severe enough to cause the individual to be unable to appreciate the wrongfulness of their acts. Some states have added a volitional component to their insanity defense. This prong deals with if an individual, as the result of a threshold condition, lacks the substantial capacity to conform their conduct to the law. However, it must be noted that the insanity defense is unpopular with many state legislatures. Four states (Idaho, Kansas, Montana, and Utah) have abolished the insanity defense. Forensic psychiatrists and psychologists are often tasked with conducting these retrospective evaluations. This is a difficult task, as it requires the forensic practitioner to reconstruct an individual’s mental state as it relates to the alleged criminal act days, months, or even years after the event. To conduct these evaluations properly often requires a substantial amount of collateral information, including previous mental health records, academic records, employment records, and, most recently, information gleaned from social media, that can assist the evaluator in the reconstruction of an individual’s mental state. This bibliography emphasizes the complexity of the insanity defense and its complicated and lengthy history. However, readers are encouraged to further explore articles and books to elucidate the lengthy legal history of the insanity defense and complexities in conducting insanity evaluations.

General Overviews

These overviews focus primarily on mental health issues and how the courts have handled, and in many respects failed to handle, them. Some cover broad aspects relative to mental illness and the law and incorporate specific aspects of the insanity defense. Erickson and Erickson 2008, a book on mental illness, focuses on the criminalization of the mentally ill, with a specific chapter (chapter 4) dedicated to the insanity defense. Likewise, Finkel 1988 discusses many of the controversies that accompany the insanity defense. In a different and unique take, Ewing 2008 provides examples from several high-profile cases that are highly informative for understanding the inner workings of the insanity defense. Slovenko 1995 provides an overview of the insanity defense and its many complications. It also provides information useful to the testifying clinician. Sadoff 1989 is a chapter underscoring the necessity of maintaining the insanity defense for fundamental fairness; it deals with misperceptions of the insanity defense.

  • Erickson, P. E., and S. K. Erickson. 2008. Crime, punishment, and mental illness: Law and the behavioral sciences in conflict. New Brunswick, NJ: Rutgers Univ. Press.

    This book focuses on the problem of the criminalization of mental illness and how individuals with mental illness populate the penal system. This book has clear implications for the insanity defense, and chapter 4 focuses on the conflict and difficulty of the insanity defense.

  • Ewing, C. P. 2008. Insanity: Murder, madness, and the law. New York: Oxford Univ. Press.

    DOI: 10.1093/acprof:oso/9780195326130.001.0001

    This book reviews ten cases of insanity that cover a variety of topics. These high-profile cases are highly informative for when considering how case law has developed and the implementation of the insanity defense on legal cases.

  • Finkel, N. J. 1988. Insanity on trial. New York: Plenum Press.

    DOI: 10.1007/978-1-4613-1665-7

    In this book, Finkel deals with many of the controversies of the insanity defense. He has chapters on specific issues and the book provides an overview of the insanity defense and its contentiousness.

  • Sadoff, R. L. 1989. In defense of the insanity defense. In Criminal court consultation. Critical Issues in American Psychiatry and the Law 5. Edited by R. Rosner and R. B. Harmon, 111–118. New York: Plenum Press.

    Sadoff authored a chapter underscoring the necessity of maintaining the insanity defense for fundamental fairness, and dealing with misperceptions of the insanity defense.

  • Slovenko, R. 1995. Psychiatry and criminal culpability. New York: John Wiley & Sons.

    The focus of this book is on the insanity defense and its complications. It also deals with assessments of criminal responsibility and culpability and the psychiatrist (and psychologist) as an expert witness.

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