Law is the system of rules and regulations created by a society that sets limits on its members’ behavior. These rules are enforced by mechanisms such as police and courts, and sanctions (fines, imprisonment) can be imposed on people who break the laws. There are many different kinds of laws: for example, copyright protects the rights of people over their artistic work, patent law covers inventions, and trust law sets out the rules for money that is saved and invested.
In most countries with a modern written constitution, laws are written and voted on by groups of politicians in legislatures such as parliaments or congresses that are elected by the governed peoples. However, there are still some countries which use a law of the jungle type of rule where laws are determined by judges who hear cases on an ad hoc basis and make up their own laws. These are called common law systems.
To determine “what the law is” on a particular topic, the judge hearing the case must first ascertain the facts. Then they must locate any relevant statutes and previous decisions on the topic. From those decisions they must extract principles, analogies and statements about what the law is, and finally they must reason from those principles to a set of specific factual circumstances. This process is known as stare decisis and is the foundation of legal reasoning in all countries that have a common law system.