The defense is controversial, and the rules for its legal usage vary from state to state.

(1) The M’Naghten Rule (26 states including Florida) is commonly known as the “right vs. wrong” test. It is strict, based on the fact that “every man is presumed to be sane.” Most defendants have the burden of proving they didn’t know what they were doing was wrong.

(2) The Irresistible Impulse Test (rarely used now) was a response to criticism that the M’Naghten Rule was too strict. If defendant would have committed the crime even if there was “a policeman at his elbow” he must have been acting under an irresistible impulse.

(3) The Durham Rule (only in New Hampshire) expanded psychological evaluation by adding “diminished capacity” to the insanity defense. Defendant was not guilty if his unlawful act was the product of a mental disease or defect.

(4) The ALI Model Penal Code (19 states) combines the other tests. Defendant isn’t responsible for a crime if “at the time of such conduct as a result of a 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.”

(5) The current trend: The insanity defense acquittal of John Hinckley’s attempted assassination of President Reagan so outraged the public it started a backlash where the defense was legally abolished in Idaho, Kansas, Montana and Utah. It led to the Federal Insanity Defense Reform Act of 1984. States also toughened insanity defense laws by re-emphasizing the M’Nagthen rule, shifting the sanity burden of proof, adopting “guilty but mentally ill” defenses, and restricting institutional commitment and release procedures.

Ask Doctor Law appears the first Monday of the month in Business Monday. Send questions to askdoctorlaw@yahoo.com. Martin E. Segal, a licensed attorney, lectures in business law at the University of Miami School of Business Administration.

Disclaimer: This column is not intended to solicit legal business or furnish self-help legal advice. Laws vary from state to state. Readers are strongly urged to consult independent and qualified legal professionals before making any business decisions. The views expressed are those of the writer and not of The Miami Herald.