substantial capacity test
substantial-capacity test. Criminal law. The Model Penal Code’s test for the insanity defense, stating that a person is not criminally responsible for an act if, as a result of a mental disease or defect, the person lacks substantial capacity either to appreciate the criminality of the conduct or to conform the conduct to the law. • This test combines elements of both the McNaghten rules and the irresistible-impulse test by allowing consideration of both volitional and cognitive weaknesses. This test was formerly used by the federal courts and many states, but since 1984 many jurisdictions (including the federal courts) — in response to the acquittal by reason of insanity of would-be presidential assassin John Hinckley — have narrowed the insanity defense and adopted a new test resembling the McNaghten rules, although portions of the substantial-capacity test continue to be used. Model Penal Code § 4.01. — Also termed Model Penal Code test; MPC test; American Law Institute test; ALI test. See INSANITY DEFENSE. [Cases: Criminal Law 48.]
