Not Guilty by Reason of Insanity – based on the insanity defense

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not guilty by reason of insanity:

1. A criminal defendant’s plea of not guilty that is based on the insanity defense. — Abbr. NGRI. — aka not guilty on the ground of insanity.

insanity defense Criminal law. (1912) An affirmative defense alleging that a mental disorder caused the accused to commit the crime.  See 18 USCA § 17; Fed. R. Crim. P. 12.2.  *  Unlike other defenses, a successful insanity defense may not result in an acquittal but instead in a special verdict (“not guilty by reason of insanity”) that usually leads to the defendant’s commitment to a mental institution. — aka insanity plea.

  • insanity – a mental disorder severe enough to prevent a person from having legal capacity, excusing them from criminal or civil responsibility; constitutes an insanity defense.
  • black-rage insanity defense (1995) An insanity defense based on an African-American’s violent eruption of an er induced at least partly by racial tensions.  *  This defense was first used in the mid-1990s.

Various Tests used to Determine Sanity:

appreciation test – requires clear, convincing evidence that at the time of the crime, the defendant suffered from a severe mental disease or defect preventing them from appreciating the wrongfulness of the conduct. Established via the Insanity Defense Reform Act of 1984: 18 USCA § 17. — aka Insanity Defense Reform Act of 1984 test.

Currens test – requires no more than the jury must be satisfied that as a result of mental disease or defect, the accused lacked substantial capacity to conform his conduct to the requirements of the law.

Durham test – holds that a defendant is not criminally responsible for an act that was the product of mental disease or defect. — aka Durham rule; product test.

McNaghten test – the “right and wrong test” to determine a person’s sanity. — aka McNaghten rule; right-and-wrong test; right-wrong test.

substantial-capacity test – the Model Penal Code’s test for the insanity defense; determines if the person lacks substantial capacity to appreciate the criminality of the conduct or to conform their conduct to the law. Model Penal Code § 4.01. — aka Model Penal Code test; MPC test; American Law Institute test; ALI test.


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[1]: Black’s Law Dictionary Deluxe Tenth Edition by Henry Campbell Black & Editor in Chief Bryan A. Garner. ISBN: 978-0-314-62130-6

[2]: Ballantine’s Law Dictionary with Pronunciations
Third Edition
 by James A. Ballantine (James Arthur 1871-1949).  Edited by William S. Anderson.  © 1969 by THE LAWYER’S CO-OPERATIVE PUBLISHING COMPANY.  Library of Congress Catalog Card No. 68-30931

[3]:  Ballantine’s Law Dictionary Legal Assistant Edition
by Jack Ballantine 
(James Arthur 1871-1949).  Doctored by Jack G. Handler, J.D. © 1994 Delmar by Thomson Learning.  ISBN 0-8273-4874-6.

[4]: Rollin M. Perkins & Ronald N. Boyce, Criminal Law 959-60 (3d ed. 1982).


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