Criminal law in the Anglo-American system of jurisprudence is based upon the concept that persons should be held responsible for their acts. A strong corrollary to this idea is that certain types of persons, namely the "insane," should not be held responsible for criminal conduct. Although this proposition seems beautifully simple, courts in England and the United States for over a hundred years have wrestled with the problem of what constitutes insanity, or, to phrase it more accurately, what type of mental condition should preclude responsibility for a criminal act.
Mary L. Ryan,
Criminal Law - Reexamination of Tests for Criminal Responsibility,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol53/iss7/4