Insanity is defined in a standard dictionary as "more or less permanent derangement of one or more psychical functions, due to a disease of the mind" (Stein, 1979, p. 735). However, in law, such derangement need not always be permanent in order to relieve an individual from standing trial for an offense alleged to have been committed by the individual (Morse, 1978), to absolve an individual from responsibility for an act committed by the individual (Hardisty, 1973) or to relieve a condemned individual from execution ("Insanity of the Condemned," 1979).
There is disagreement about the meaning of insanity and about whether an individual's condition should ever be characterized as insanity (Redlich, 1952,; A Psychiatric Glossary, 1964). The legal definition of insanity was originally derived from the medical profession (Hardisty, 1973). Within the judicial system, there are differences in interpretation (Dershowitz, 1973) and application of tests of insanity (Goldstein, 1973) and conflicts about the desirability of the use of insanity as a legal defense (Moore, 1980).
Regardless of the disagreement surrounding the issue of insanity in both law and psychology, insanity remains a legal defense in certain cases of criminal law (Floud, 1974). Different tests of legal insanity are applied in different jurisdictions (Fingarette, 1972). The most widely applied legal test of insanity is the M'Naghten rule, which dates from 1843 in the United Kingdom and is now used in most of the states of the United States (Hardisty, 1973; Moore, 1980).
This research will survey the adequacy of the M'Naghten rule as a determinant of insanity in the context of criminal law in the 1980s. This examination will be divided into four sections: the rationale and purpose of the use of insanity as a defense; the most widely used tests of insanity in the United States; controversies surrounding the use of insanity as a defense; and an evaluation of th...