This is an aspect of a more general insanity defense (see the M'Naghten rules). The defense "was first recognized by Scottish common law to reduce the punishment of the "partially insane"." It developed from the practice of juries in the 19th century of returning verdicts of guilty with a recommendation as to mercy or mitigation of sentence to reflect any extenuating circumstances. In a series of decisions, given mainly by Lord Deas, a doctrine grew that various types of mental weakness could have the effect of reducing what would otherwise be a conviction for murder (which attracted capital punishment) to one for culpable homicide (where the courts had greater discretion in sentencing). An example of a "diminished capacity" might be extremely low intelligence. In the English case of "R v Raven", a man who had a physical age of 22 years but a mental age of only 9 years felt provoked by homosexual advances and killed his perceived attacker. His mental deficiency was not in dispute and, since a child of 9 years would not have been criminally responsible (see s50 Children and Young Persons Act 1933), and his mental responsibility for his acts was substantially impaired, manslaughter was the only realistic verdict. The rationale of the defense is that, as a precondition to punishment, the criminal law requires conduct to be voluntary. If something interferes with the capacity of the individual to choose to break the law, this should be reflected by an excuse or exculpation. The law should balance the need to be fair to the individual wrongdoer, but equally offer some protection to society from a person who may not have complete control over their behavior.