n. in a criminal prosecution, a defense by the accused that he/she was briefly insane at the time the crime was committed and therefore was incapable of knowing the nature of his/her alleged criminal act. Temporary insanity is claimed as a defense whether or not the accused is mentally stable at the time of trial. One difficulty with a temporary insanity defense is the problem of proof, since any examination by psychiatrists had to be after the fact, so the only evidence must be the conduct of the accused immediately before or after the crime. It is similar to the defenses of "diminished capacity" to understand one's own actions, the so-called "Twinkie defense," the "abuse excuse," "heat of passion" and other claims of mental disturbance which raise the issue of criminal intent based on modern psychiatry and/or sociology. However, mental derangement at the time of an abrupt crime, such as a sudden attack or crime of passion, can be a valid defense or at least show lack of premeditation to reduce the degree of the crime. See also: crime defense diminished capacity insanity intent

The insanity defense, also known as the mental disorder defense, is an affirmative defense by excuse in a criminal case, arguing that the defendant is not responsible for their actions due to an episodic or persistent psychiatric disease at the time of the criminal act. This is contrasted with an excuse of provocation, in which the defendant is responsible, but the responsibility is lessened due to a temporary mental state.

n. plea in court of a person charged with a crime who admits the criminal act, but whose attorney claims he/she was so mentally disturbed at the time of the crime that he/she lacked the capacity to have intended to commit a crime. Such a plea requires that the court set a trial on the issue of insanity alone either by a judge sitting without a jury or by a jury. A finding of insanity will result in a verdict of "not guilty," but, if the condition still exists, it may result in incarceration in a mental facility for the criminally insane or confinement in a mental hospital. If the insanity no longer exists (temporary insanity), the judge has the option to require some psychological therapy, but the treatment varies from state to state. This is not the same as insane at time of trial and thus incompetent to stand trial, which will postpone trial (in all likelihood forever) pending recovery while the defendant is confined to a mental facility. See also: incompetent insanity insanity defense not guilty temporary insanity