In criminal law, a disease, defect, or condition of the mind that renders one unable to understand the nature of a criminal act or the fact that it is wrong. Tests of insanity are not intended as medical diagnoses but rather only as determinations of whether a person may be held criminally responsible for his or her actions. The most enduring definition of insanity in Anglo-American law was that proposed by Alexander Cockburn (1843). Many U.S. states and several courts have adopted a standard under which the accused must lack “substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law.” Some states have abolished the insanity plea, and others allow a finding of “guilty but mentally ill.” See also diminished responsibility.

This entry comes from Encyclopædia Britannica Concise.
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