INSANITY DEFENSE
A defense asserted by an accused in a criminal
prosecution to avoid liability for the commission of
a crime because, at the time of the crime, the per-
son did not appreciate the nature or quality or
wrongfulness of the acts.
The insanity defense is used by criminal
defendants. The most common variation is cog-
nitive insanity. Under the test for cognitive
insanity, a defendant must have been so
impaired by a mental disease or defect at the
time of the act that he or she did not know the
nature or quality of the act, or, if the defendant
did know the nature or quality of the act, he or
she did not know that the act was wrong. The
vast majority of states allow criminal defendants
to invoke the cognitive insanity defense.
Another form of the insanity defense is voli-
tional insanity, or IRRESISTIBLE IMPULSE.A
defense of irresistible impulse asserts that the
defendant, although able to distinguish right
from wrong at the time of the act, suffered from
a mental disease or defect that made him or her
incapable of controlling her or his actions. This
defense is common in crimes of vengeance. For
example, suppose that a child has been brutally
assaulted. If an otherwise conscientious and
law-abiding mother shoots the perpetrator, the
mother may argue that she was so enraged that
she became mentally ill and incapable of exert-
ing self-control. Very few states allow the voli-
tional insanity defense.
The insanity defense should not be confused
with INCOMPETENCY. Persons who are incom-
petent to stand trial are held in a mental institu-
tion until they are considered capable of
participating in the proceedings.
The insanity defense also should be kept
separate from issues concerning mental retarda-
tion. The U.S. Supreme Court ruled in 2002 in
ATKINS V. VIRGINIA, 536 U.S. 304, 122 S. Ct.
2242, 153 L. Ed. 2d 335 (2002) that the execution
of mentally retarded criminals constituted
“cruel and unusual punishment” and that it was
prohibited by EIGHTH AMENDMENT. But if a
person is acquitted by reason of insanity, execu-
tion is not an option.
The insanity defense reflects the generally
accepted notion that persons who cannot appre-
ciate the consequences of their actions should
not be punished for criminal acts. Most states
regulate the defense with statutes, but a few
states allow the courts to craft the rules for its
proper use. Generally, the defense is available to
a criminal defendant if the judge instructs the
jury that it may consider whether the defendant
was insane when the crime was committed. The
judge may issue this instruction if the defendant
has produced sufficient evidence at trial to jus-
tify the theory. Sufficient evidence invariably
includes EXPERT TESTIMONY by psychologists
and psychiatrists.
When invoking insanity as a defense, a
defendant is required to notify the prosecution.
In some states, sanity is determined by the judge
or jury in a separate proceeding following the
determination of guilt or innocence at trial. In
other states, the defense is either accepted or
rejected in the verdict of the judge or jury. Even
if evidence of insanity does not win a verdict of
not guilty, the sentencing court may consider it
as a mitigating factor.
History
“Complete madness” was first established as
a defense to criminal charges by the common-
law courts in late-thirteenth-century England.
By the eighteenth century, the complete mad-
ness definition had evolved into the “wild beast”
test. Under that test, the insanity defense was
available to a person who was “totally deprived
of his understanding and memory so as not to
know what he [was] doing, no more than an
infant, a brute, or a wild beast” (Feigl 1995, 161).
By 1840, most jurisdictions had refined the
wildbeast test to cognitive insanity and supple-
mented that with irresistible impulse insanity.
However, in 1843, a well-publicized assassina-
tion attempt in England caused Parliament to
eliminate the irresistible impulse defense.Daniel
