In law , a precedent or authority is a legal case that established a principle or rule that a court may need to adopt when deciding subsequent cases with similar issues or facts . In common law legal systems , a precedent or authority is a legal case establishing a principle or rule that a court or other judicial body may utilize when deciding subsequent cases with similar issues or facts . Black 's Law Dictionary defines `` precedent '' as a `` rule of law established for the first time by a court for a particular type of case and thereafter referred to in deciding similar cases . ''