Case law in a legal system are those laws based on previous judicial decisions. This is opposed to decisions based on existing statutes or regulations. In countries using common law, it is generally uncodified meaning there are no collections of legal rules and laws to rely on. Instead they rely on legal precedent. Precedents are previous legal cases that are used as examples for deciding the present case. They are also binding on lower courts where the facts and issues are similar. In countries that use civil law, their laws are codified and there is much less reliance on case law.
Judges make judicial decisions based on precedent and their own understanding when there are few or no precedents. This is "judge-made law" as compared to statuary law, which is made by ledislatures and governments. In the United States the courts can rule statutes and regulations unconstitutional if they go beyond the authority given by the constitution. In the United Kingdom judge-made law or common law cannot rule against statutes made by an act of Parliament. The judiciary and legislative branches are not coequal. Judges, however, have traditionally used one of three ways of interpreting statutes:
- They may be interpreted literally or simply as the law was written.
- They may use the "golden rule" meaning that if the law is difficult to interpret the judiciary may use a less obvious meaning.
- They may apply the "mischief rule". If the act lends itself to more than one interpretation, choose the interpretation that best deals with the problem.
Judges make decisions by decisions based on the appropriate laws. The judge first brings the formal charges against the accused. They then investigate to learn all the facts. Finally they make a decision. Under civil law, judiciary decisions are not a critical part of forming civil laws. Under Dutch civil law for example, there are so many civil laws that it becomes difficult for lawyers and judges to know if they have found all the laws that apply to a case. Even with all the laws, not every situation is covered. The civil court will research everything it can on the subject, then make a decision. For this reason those who start a legal case never know for certain what the decision will be.
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