The history of legal systems is the study of why and how laws have changed and evolved over time. Legal history also works within the larger context of global history and closely related to the evolution of civilizations. Throughout human history, legal systems have developed and been refined to protect both rights and freedoms and to ensure communal harmony and order.
The study of legal history has many characteristics which make it uniquely important to historians and social scientists. Unlike many other areas of history, the history of legal systems has very little left in common with other fields. What researchers can learn about legal history, however, is how changes in legal systems across various time periods affect societies as a whole and how these legal systems interact with one another.
Legal historians must be sociological researchers who understand how legal systems function in the day-to-day world. Legal historians should also be sociological researchers who understand how social history has shaped the modern legal history. In particular legal historians need to think about how different legal systems have been formed by ancient peoples. Legal historians should also think about how legal systems have been shaped by twentieth-century developments such as the legal theories of the United States, Canada and Great Britain. These nations have legal traditions that differ markedly from those of other countries.
There are four main schools of thought about the relationship between legal systems and the evolution of society. Each school of thought, which goes by the names of legal positivism, legal realism, historicism, and judicial history, believes that legal systems are largely independent and operate independently of social norms. However, all four schools of thought provide important contributions to an understanding of the relationship between the legal system and societal behavior.
One school of thought about the relationship between the legal system and society, and the development of legal norms, is called legal positivism. This school maintains that legal systems and courts function primarily as established mechanisms for helping society to solve social problems. The proponents of legal positivism claim that legal systems are established through the application of "common law", that is, statutes and case law that have universal application. Because of the exclusivity of the application of "common law" and the exclusivity of cases and statutes in English Common Law, legal positivism maintains that it is not possible for a person to change or alter laws that have been decided in a specific court case based on facts that are found outside that court.
Another school of thought about the relationship between legal systems and society is called the judicial history of ideas. This school believes that the ideas and theories that have been developed by legal professionals throughout history have shaped the way that courts have interpreted case law and the principles that underlie that law. These concepts have often been viewed as a source of protection for people from oppressive actions and laws. For example, the principle that "innocent until proven guilty" has been used to justify practices such as imprisonment without trial, and the use of torture.