A common law state is a term that refers to a national or local state government whose legal system is based on and derived from English common law. It was known as common law because when deciding legal matters, judges relied on what was traditionally considered the common custom of the land. Over time, these common customs and traditions formed the basis of the written laws and statutes in England. The use of common law is in contrast to civil law, which forms the basis of the legal systems in the majority of the world’s nations and is based on the legal system of the Roman Empire.
Today the term common law is often used to refer to a legal tradition that places a large amount of weight and authority on legal precedence established during previous court cases. In a common law state, a judge or court would use previous rulings and decisions as a determining guide when ruling or deciding on a current case. Therefore, the rulings or conclusions of one judge or court may influence the rulings and conclusions of another judge or court.
This does not mean, however, that judges in a common law state would only base their decision on legal precedent. On some occasions, courts may render decisions that overturn long standing precedent. When this occurs, the decision forms a new legal precedent that future courts will use as the basis of their decisions. This feature often makes the legal system in a common law state more fluid than civil law systems.
In a pure civil law system, judges do not typically use legal precedent to form their decisions. Rather, judges in a civil law state review the specific laws and statutes that are relevant to the case and interpret the intent of the law in making their decision. In a civil law state the ruling of one judge or court may have no effect on the ruling on another judge or court.
Common law is used primarily in areas that were once part of the British Empire, such as the United States, or are currently part of the British Commonwealth, such as Canada, Australia, South Africa, Singapore and the United Kingdom. However, in the United States and Canada there are areas that do not use common law as the sole basis of their local legal systems. The U.S. state of Louisiana and the Canadian province of Quebec both use a legal system that is generally based on civil law. Both Louisiana and Quebec were once French possessions and their legal systems were influenced by the Code Napoleon, which in turn was based on Roman civic law.