The Famous Insanity Defense

The insanity defense is a favorite on television and in the movies in attempting to relieve criminal defendants of punishment for their acts. The test in the majority of States is known as the M’Naghten test: the standard is whether at the time of the conduct in question the defendant lacked the ability to know the wrongfulness of his actions or understand the nature and consequences of his acts; the product of their incapacity must be the product of mental disease or defect. This is a purely cognitive test. Another test used by some jurisdictions is the “irresistible impulse” rule: the standard is due to mental disease or defect the defendant lacked the capacity for self control or free choice. This is a volitional test. Finally, the Model Penal Code test, an authority in the field of criminal law, uses broader language and is both cognitive and volitional. This test requires that the defendant lacked substantial capacity to appreciate the criminality of his conduct or to conform his conduct to the requirements of law. If the defense attorney is successful in proving one of these three tests (depending on which test the jurisdiction uses) then the defendant may be successful in asserting an insanity defense.