There are obvious limits to this power of developing unwritten
law. The courts are not to push forward into a place more
appropriate for the legislature to occupy.

Mr. Justice Holmes of the Supreme Court of the United States,
when Chief Justice of Massachusetts, stated with his usual
elegance and force the bounds within which, as it seemed to him,
judicial authority should be kept. In a common law suit against
a railroad company for damages suffered by an accident on its
road, the defendant had asked the trial court to order the
plaintiff to submit to an examination of his person by a
physician whom it named, for the purpose of determining what
injuries he had really suffered. "We agree," said the Chief
Justice, "that in view of the great increase of actions for
personal injuries it may be desirable that the courts should have
the power in dispute. We appreciate the ease with which, if we
were careless or ignorant of precedent, we might deem it
enlightened to assume that power. We do not forget the
continuous process of developing the law that goes on through the
courts in the form of deduction or deny that in a clear case it
might be possible even to break away from a line of decisions in
favor of some rule generally admitted to be based upon a deeper
insight into the present wants of society. But the improvements
made by the courts are made, almost invariably, by very slow
degrees and by very short steps. Their general duty is not to
change, but to work out, the principles already sanctioned by the
practice of the past. No one supposes that a judge is at liberty
to decide with sole reference even to his strongest convictions
of policy and right. His duty in general is to develop the
principles which he finds with such consistency as he may be able