American Law Institute Rule

n.
  1. A 1962 US rule used as a test of criminal responsibility and stating that an individual accused of a crime is not criminally responsible if at the time of such conduct as a result of mental disease or defect the person lacks substantial capacity either to appreciate the wrongfulness of the conduct or to conform such conduct to the requirements of law.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.