Ovid's Metamorphoses

Ovid's metamorpheses........The claim of irresistible impulse is a defense in some jurisdictions. The irresistible impulse tests asks if, at the time the crime was committed, a mental disease or disorder prevented the defendant from controlling his or her behavior.

The Durham Rule, also known as the product rule, holds that an accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect.

The American Law Institute’s substantial capacity test, which is incorporated into the Model Penal Code, says that a person is not responsible for criminal conduct if at the time of such conduct, and as a result of mental disease or defect, he lacks substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law.

A guilty but mentally ill verdict (GBMI) establishes that a defendant, although mentally ill, was sufficiently in possession of his faculties to be morally blameworthy for his acts.

The defense of diminished capacity, also called diminished responsibility, is available in some jurisdictions. It is based upon claims that a defendant’s mental condition at the time of the crime, although not sufficient to support the affirmative defense of insanity, might still lower criminal culpability. A finding of diminished capacity may result in a verdict of "guilty" to lessened charges.

The insanity defense is not widely used, and is raised in only about 1% of all criminal cases. Defendants found "not guilty by reason of insanity" are rarely set free, being instead committed to a mental hospital until confinement is no longer deemed necessary.

Because of the difficulties associated with assessing insanity from a legal perspective, a number of jurisdictions have eliminated the insanity defense.