Commercial outlines and secondary sources are best used as supplements in this instance if you are having trouble extracting the rule. Scholars collect the common law into volumes called the Restatements. Congress or state legislatures write statutes, which results in laws that are primarily influenced by special interest groups. A body of law is sometimes collected in a model code or uniform statute , such as the Uniform Commercial Code or the Model Penal Code. In your first year of law school, you'll primarily be focused on the common law.
Common law is judge-made law.
Judges base their decisions on principles that have developed over time within the judicial system. The rule itself is really just a series of definitions. If the facts of the case fit within the definition, then the rule applies. The model codes are an attempt by the legal scholars and the federal government to have consistent laws between different states. The state legislature may adopt the model code as its base, then amend it to conform with the common law traditions in that state.