Law
Common law and equity

In common law legal systems, decisions by courts are explicitly acknowledged as "law" on equal footing with legislative statutes and executive regulations. The "doctrine of precedent", or stare decisis (Latin for "to stand by decisions") means that decisions by higher courts bind lower courts to assure that similar cases reach similar results. In contrast, in civil law systems, legislative statutes are typically more detailed, and judicial decisions are shorter and less detailed, because the adjudicator is only writing to decide the single case, rather than to set out reasoning that will guide future courts.

Common law originated from England and has been inherited by almost every country once tied to the British Empire (except Malta, Scotland, the U.S. state of Louisiana, and the Canadian province of Quebec). In medieval England during the Norman conquest, the law varied shire-to-shire based on disparate tribal customs. The concept of a "common law" developed during the reign of Henry II during the late 12th century, when Henry appointed judges that had authority to create an institutionalised and unified system of law common to the country. The next major step in the evolution of the common law came when King John was forced by his barons to sign a document limiting his authority to pass laws. This "great charter" or Magna Carta of 1215 also required that the King's entourage of judges hold their courts and judgments at "a certain place" rather than dispensing autocratic justice in unpredictable places about the country. A concentrated and elite group of judges acquired a dominant role in law-making under this system, and compared to its European counterparts the English judiciary became highly centralised. In 1297, for instance, while the highest court in France had fifty-one judges, the English Court of Common Pleas had five. This powerful and tight-knit judiciary gave rise to a systematised process of developing common law.

As time went on, many felt that the common law was overly systematised and inflexible, and increasing numbers of citizens petitioned the King to override the common law. On the King's behalf, the Lord Chancellor started giving judgments to do what was equitable in a case. From the time of Sir Thomas More, the first lawyer to be appointed as Lord Chancellor, a systematic body of equity grew up alongside the rigid common law, and developed its own Court of Chancery. At first, equity was often criticised as erratic. Over time, courts of equity developed solid principles, especially under Lord Eldon. In the 19th century in England, and in 1937 in the U.S., the two systems were merged.

In developing the common law, academic writings have always played an important part, both to collect overarching principles from dispersed case law, and to argue for change. William Blackstone, from around 1760, was the first scholar to collect, describe, and teach the common law. But merely in describing, scholars who sought explanations and underlying structures slowly changed the way the law actually worked.
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