The author, a professor of law and criminology, argues that the special plea of unfitness or incompetency to stand trial, as well as the insanity defense, should be abolished. It has been assumed that although the mentally ill commit crimes, they are less guilty in moral terms. However, government does not have the competence to assess moral worth and should not attempt to do so. When the mentally ill are made as fit as possible, they should be tried, despite their illness or retardation, under special rules dealing with pretrial disclosure, onus and burden of proof, corroborations, jury directions, and new trials appropriate to particular circumstances. At sentencing, mental illness should normally reduce the severity of punishment, except in certain cases; the author suggests when to mitigate punishment, when to aggravate it, and the proper limits of both. Justice does not require the imposition of identical sentences on those who have inflicted equal harm and have identical guilt. Two works of fiction are included as a frame of reference for the discussion. Footnotes and an index are supplied.