Defining Mental Illness 165conditions such as mental retardation, substance abuse, and epilepsy (Levy &
Rubenstein, 1996; Melton et al., 1987). Additionally, alcohol and substance abuse
problems are generally not considered a mental illness for legal purposes. Thus,
by excluding some mental impairments the law has limited the scope of mental
illness to some degree. The meaning of mental illness nonetheless remains open to
individual interpretation. Who, then, interprets?
The consistent imprecision with and neglect for operationalization by the legisla-
ture has left the courts to "fashion a definition for the words 'mentally ill'... thereby
till[ing] the void in the statutory hospital law" (Dodd v. Hughes, 1965, p. 542). With
the responsibility of defining and assessing potential mental illness as it stands be-
fore them, the courts have further deferred to the profession of mental health
(i.e., expert testimony by psychiatrists and psychologists) (Arrigo, 1993; Melton
eta!., 1987; Reisner& Slobogin, 1990). This power given to, or, more appropriately,
dependent on, the medical and mental health communities in the decision-making
process persists, even though substantial research has documented lack of consen-
sus among professionals in matters of diagnosis (Arrigo, 1993). Research has shown
that psychologists and psychiatrists are not necessarily any more in agreement about
what mental illness is than anyone else. Thus, the failure to legally define mental
illness may be, in part, a function of psychology and medicine's lack of precision in
defining and describing it.Insanity Defense
The various insanity defenses (tests) can only be used by individuals suffering from
a mental disease or defect. In order to be "excused" from criminal behavior, the
individual must not only be mentally ill, but the mental illness must directly cause a
dysfunction which is relevant when the offense was committed (Melton et al., 1987).
Again, the meaning of "mental illness" becomes the key issue. Melton et al. note that
with mental illness being imprecisely defined, it would seem that "any mental dis-
ability that causes significant cognitive or volitional impairment will meet the thresh-
old f of mental illness needed for insanity defenses]" (p. 199). Historically, however,
the successful insanity defenses have generally arisen from individuals who were
suffering from a psychosis or mental retardation. Studies suggest that 60—90% of de-
fendants acquitted for reasons of insanity have been psychotic (Melton et al., 1987).
Very few case opinions attempt to define mental disease or defect. The few cases
that have, however, define the concept narrowly In other words, the courts have
shown a general disapproval of many conceptions of insanity including mildly psy-
chotic individuals, dissociative disorders, and drug- and alcohol-induced insanity
(Melton et al., 1987). Further, the American Psychiatric Association (APA) has de-
fined "mental disease or defect" in a narrow sense, suggesting it should only include
"severely abnormal mental conditions that grossly... impair a person's perception
or understanding of reality" (APA, 1983). Other evidence, however, would suggest
that, in reality, the conception of mental illness by the courts is more elastic. In