Common law is a term in law that traces its origins back to England and was introduced in the 12th century. Common law refers to a legal system that depends on previous rulings or precedents to make decisions on new and similar cases. Thus, a decision to a case is determined based on existing decisions concerning cases of a similar nature. Decisions in a case determined to be different from previous cases form the case law or precedent for similar future cases.

The system found its way to the United States and remains active in some jurisdictions, especially in the southwestern states. However, it should be noted that a blend of civil law and common law is used in the United States. Civil law applies to cases where statutes are available, while common law is applicable in instances where statutory laws remain silent or are unavailable.

Currently, criminal cases are exclusively determined based on statutory laws at the federal level following the Supreme Court determination in United States v. Hudson and Goodwin. However, common law remains applicable in some states and is relied upon to determine cases where similar statutory crimes do not exist. It should be noted that most criminal statutes have their basis in common law. In states where criminal statutes are not clear on legal definitions, the court is forced to revert to the available common law description.

Discussions of common law more frequently occur in the context of civil procedures, but there is a history of its interaction with and influence on the evolution of criminal law in the United States.  Common law, of course, is derived from legal precedents established over many years and which build upon each other.  In contrast, the U.S. criminal justice system derives primarily from laws passed by legislatures at the federal and state levels.  There has been no shortage of legal scholars and social activists who have pronounced a strong preference for a justice system based upon common law as opposed to one predicated upon legislative action.  Judge Richard Posner, who has written widely on the issue, especially during his earlier career as a professor of law, believes that legal restraints derived from common law are more “economical” than those that originate in a parliamentary system, which by nature involves a far more expansive and costly process and risks lacking the wisdom that emanates from the benches of experienced jurists.  [See Posner’s Economic Analysis of Law, 1973 (First Edition)]  Over time, however, the influence of common law on criminal justice in the United States has diminished. 

While the English tradition of common law successfully crossed the Atlantic, the founders of the United States opted to establish the constitutional system that governs the country today.  While common law has been largely usurped by statutory provisions passed by Congress, some examples of English common law survive today.  One involves the notion of an insanity defense in criminal cases.  Another example is the continued importance of “precedence” in both criminal and civil procedures.  Reference to legal precedents is a cornerstone of the conduct of criminal trials, and provides a legal linkage to the nation’s colonial origins.  U.S. sodomy laws also have their origin in English common law.  Common law, while playing an important role in the development of criminal and civil justice systems in the United States, remains far more significant in civil law than in criminal law.  The federal and 50 state governments prefer to weigh-in on matters of personal conduct, as the system of government set forth in the U.S. Constitution established the three branches of government precisely so that law would more directly reflect the will of the people and not that of professional jurists.