There are three main differences between common law and statutory law. Common law is based on precedent, or case law. Statutory law is written law as decided by the legislature or other government agency. The main differences are how the laws are created and the basis of challenges.
Under common law, new laws are created through the decisions made by judges. When the judges are listening to a case, they are making decisions based on the decisions made in previous cases. In situations where no specific applicable law can be found, the decision the judge makes then become law.
Lawyers preparing to argue a case must make submissions to the court for decisions on different items based on case or common law and statutory laws that are applicable. If the plaintiff or the defendant decides to appeal the decision, they must make an argument to the appeals court. The submission must list the objections to the decision based on prior law or legal procedures.
Statutory laws are those made by the government of a country. There are several reasons to issue these types of law: to meet citizens needs, to formalize existing law or resolve an outstanding issue that the courts refer to the government. The government has a clear role in determining the laws and punishments that are appropriate for their country.
Statutory laws can be issued by a variety of government agencies and their jurisdictions and effective dates can vary quite widely. In addition to laws issued by federal and state governments, cities and towns can also create their own municipal ordinances, bylaws or regulations. All these items have the power of a law. These multiple sources of legal guidelines adds to the complexity and possible conflicts within the law.
There are quite a number of countries that have a combination of statute and common law. The most important job when practicing law is to keep up to date when decisions are made that impact on your area of practice. Decisions can strike down old laws, or create possible avenues of appeal for prior cases.
The job of a legal researcher is to assist the lawyers in writing their legal arguments, basing them on a combination of case and statutory law. They must also prepare a list of possible objections or rebuttal arguments from the opposing legal team. These items, along with the details of the case, determine the legal strategy.