Overruling is the procedure whereby a court higher up in the hierarchy sets aside a legal ruling established in a previous case.
It is strange that, within the system of stare decisis, precedents gain increased authority with the passage of time. As a consequence, courts tend to be reluctant to overrule longstanding authorities even though they may no longer accurately reflect contemporary practices or morals.
While old principles are not usually good in dentistry or computer science, they are often seen that way in law. In addition to the wish to maintain a high degree of certainty in the law, the main reason for judicial reluctance to overrule old decisions would appear to be the fact that overruling operates retrospectively, with the effect that the principle of law being overruled is held never to have been law. It may even lead to the imposition of criminal liability on previously lawful behaviour. It has to be emphasised, however, that the courts will not shrink from overruling authorities where they see them as no longer representing an appropriate statement of law. The decision in 1989 to recognise the possibility of rape within marriage may be seen as an example of this.
The courts are rarely ready to challenge the law-making rights of Parliament in an open way and, on occasion, explicitly state that it is a matter on which Parliament should legislate.
Overruling should not be confused with ‘reversing’, which is the procedure by which a superior court in the hierarchy reverses the decision of a lower court in the same case.