The M'Naghten Rules have been the subject of critical review for over a century and represent a significant change in the insanity defense. Some believed the rules widened the definition of insanity too far, and they were fearful that many more individuals would employ the insanity defense successfully. Others believed that the rules were too restrictively formulated, thereby eliminating the insanity defense from those who should appropriately employ it. Much of the legal and psychological criticism has focused on particular words and phrases and their meanings and implications. At the center of the controversy over the rules is the phrase "to know the nature and quality of the act he was doing." Controversy also exists over the concepts of "wrong" and "disease of mind." The American Law Institute differentiates mental disease from the question of criminal responsibility. The option of guilty but mentally ill has been rejected by the American Bar Association, the American Psychiatric Association, and others because these groups feel such an option offers a compromise "easy way out" for jurors. The reaction to calls for abolishing the insanity defense from jurors and professional experts has generally been negative. It is concluded that the relation between law and psychology is critical to understanding the insanity defense.