In the legal system of the United States, a matter is moot if further legal proceedings with regard to it can have no effect, or events have placed it beyond the reach of the law. Thereby the matter has been deprived of practical significance or rendered purely academic. The U.S. development of this word stems from the practice of moot courts, in which hypothetical or fictional cases were argued as a part of legal education. These purely academic issues led the U.S. courts to describe cases where developing circumstances made any judgment ineffective as "moot". The doctrine can be compared to the ripeness doctrine, another judge-made rule, that holds that judges should not rule on cases based entirely on anticipated disputes or hypothetical facts. Similar doctrines prevent the federal courts of the United States from issuing advisory opinions.