The challenge of a society to ®nd the appropriate balance between accountability of one's criminal acts and allowance for mental illness is centuries old. Early tests of criminal responsibility are, in their core functional elements, not much dierent than today's, and tests in dierent countries are remarkably similar. (See, e.g., Babayan with Shashina, 1985 re Soviet insanity law; Briscoe et al., 1993 re English law;, Saû & von Oefele, 1990, re German law; re US insanity laws.) Criminal responsibility requires the commission of a criminal act (actus reus) and a corresponding mental state or intent (mens rea). Diminished or absent cognitive ability concerning the wrongfulness/criminality of the act, or in some cases ability to control one's behavior, can be argued to reduce or eliminate the defendant's culpability and derivatively punishment. The stability and endurance of these underlying principles is really quite remarkable.
On the other hand, insanity laws in the United States have undergone signi®cant changes in the latter half of the 20th century , and there are signi®cant dierences between countries in de®nitions of qualifying mental conditions and in the application of verdicts wherein mental conditions reduce or eliminate criminal responsibility. From individual criminal cases, to legislation, to the application of insanity and other ``mental'' verdicts, one can easily appreciate the dynamic interplay of forces competing for moral triumph.
If the M'Naghten test was essentially the ``law of the land'' in the United States for the ®rst half of the twentieth century, today the individual states collectively have a mosaic of variations of insanity law: M'Naghten test, modi®ed M'Naghten test, ALI test, modi®ed ALI test, product test, and now at least four states have no special insanity defense. Examination of expanded statutory and judicial insanity law uncovers greater variations in the extent and quality of mental disorders that explicitly qualify or do not qualify for the insanity defense.
But why should criminal defendants have the option of an insanity defense anyway? More broadly, how are mental disorders relevant to the issue of criminal responsibility? Morse ( pp. 147±164) analyzes the theoretical underpinnings of criminal law that support the consideration of mental illness in determining whether mens rea exists, and the possibility of special defenses based on mental illness. Although mental disorders should excuse criminal conduct where sucient irrationality substantially aected the defendant's ``decision'' to commit a criminal oense, Morse concludes that constitutional law has not required an insanity defense or, even more generally, a mental disorder excuse.