The insanity defense is when a defendant may be excused from criminal responsibility if at the time of the commission of the act the party accused was laboring under such a defect of reason, from a disease of the mind, as not to know the nature and the quality of the act he was doing, or if he did know it, that he did not know that he was doing what was wrong. Thus, according to the rule, a person is basically insane if he or she is unable to distinguish between right and wrong as a result of some mental disability. (Siegel, Larry J. 2001) .
Insanity is a legal, not a medical definition. Therefore, mental illness and insanity are not synonymous: only some mental illness constitutes insanity. Insanity, however, includes not only mental illness but also mental deficiencies. Due to this, there are problems in exactly how to apply a medical theory to a legal matter (Wrobleski, Henry M. and Hess, Karen M. 2000) Opponents of the insanity defense charge that criminal responsibility is separate from mental illness and the two should not be equated. They argue that it is a serious mistake to consider criminal responsibility as a trait or quality that can be detected by psychiatric evaluation. (Wrobleski, Henry M. and Hess, Karen M. 2000) The legal concepts of mental illness and insanity raise questions in a conflict between what are termed legalistic criminology and scientific criminology: mens rea (guilty mind) , punishment vs. treatment , responsibility , and prisons vs. hospitals. This debate seesaws to and from amidst a gray area between law and science. The major difficulty with a theory such as insanity is that it is just that, a theory. To scientists and philosophers theories are a way of life, but applied to the concept of law theories become somewhat dangerous. By applying a loose theory such as insanity to law we are in essence throwing the proverbial "monkey wrench" into the wheels of justice.