An optimal system of criminal justice will provide protection of the general welfare by a system of threats aimed at deterring the convicted from repeating the offense and by deterring others from emulating them. Deterrence is the impact on the motivation of possible offenders so that they are more inclined to obey the law than they otherwise would have been. "Moral/legal motivations" involve motivation not to perform actions for which the law provides sanctions, because to do so risks unpleasant consequences. The insanity defense is essentially the claim that the state of mind of the agent at the time of his/her unlawful act prevents conclusive inference from the act to a defective level of moral/legal motivation (as being its necessary condition), hence it provides a release from culpability. The basic idea of the insanity defense should be that some actual mental/brain state of the agent (not necessarily a "mental disease or defect" in some specified sense) other than the "standard" grounds for excuse could have prevented the agent from abiding by the law despite the presence of an acceptable level of moral/legal motivation. This article also discusses the disposition of persons judged not guilty by reason of insanity. 36 footnotes.