The common law originally developed under the auspices of the adversarial system in historical England from judicial decisions that were based in tradition, custom, and precedent. The form of reasoning used in common law is known as casuistry or case-based reasoning. Common law may be unwritten or written in statutes or codes. The common law, as applied in civil cases (as distinct from criminal cases), was devised as a means of compensating someone for wrongful acts known as torts, including both intentional torts and torts caused by negligence and as developing the body of law recognizing and regulating contracts. Though today common law only is generally thought of as applying to civil disputes; originally in encompassed the criminal law before criminal codes were adopted in most common law jurisdictions in the late 19th century. The type of procedure practiced in common law courts is known as the adversarial system which is also a development of the common law.
Before the institutional stability imposed on England by William the Conqueror in 1066, English citizens were governed by unwritten local customs that varied from community to community and were enforced in often arbitrary fashion. For example, courts generally consisted of informal public assemblies that weighed conflicting claims in a case and, if unable to reach a decision, might require an accused to test guilt or innocence by carrying a red-hot iron or snatching a stone from a caldron of boiling water or some other "test" of veracity. If the defendant's wound healed within a prescribed period, he was set free as innocent; if not, execution usually followed.
In 1154, Henry II became the first Plantagenet king. Among many achievements, Henry institutionalized common law by creating a unified system of law "common" to the country through incorporating and elevating local custom to the national, ending local control and peculiarities, eliminating arbitrary remedies, and reinstating a jury system of citizens sworn on oath to investigate reliably criminal accusations and civil claims. The jury reached its verdict[?] through evaluating common local knowledge, not necessarily through the presentation of evidence, a distinguishing factor from today's civil and criminal court systems.
Henry II's creation of a powerful and unified court system, which curbed somewhat the power of canonical (church) courts, brought him (and England) into conflict with the church, most famously, with Thomas Becket, the archbishop of Canterbury. Things were resolved eventually, at least for a time, in Henry's favor when a group of his henchmen murdered Becket. For its part, the Church soon canonized Becket as a saint.
By the 17th century, the judicial system recognized that certain wrongs, such as trespass, were not susceptible of compensation because the wronged person didn't care about the money but wanted his land back (trespass) or the benefit of his bargain (that house he agreed to purchase), and mere compensation could not make him whole. From this, courts of chancery developed in England with a purpose of doing what was fair ("equitable"), and through these courts one could force the wrongdoer to sell him that house or get off his land (or go to jail if he still refused). In England, courts of law and equity were combined in 1875, and the roles of the advocates appearing before them were amalgamated into one -- a solicitor. Barristers also operate in some common law courts. These systems of law (providing money damages) and equity (fashioning a remedy to fit the situation) continued as parallel systems and courts well into the 20th century in most courts in the United States: In the federal courts[?] there is no separation between law and equity; Delaware still has separate courts of law and equity, and in many states there are separate divisions for law and equity within one court.
The common law constitutes the basis of the legal systems of: the United Kingdom (except Scotland), the United States (except Louisiana, California and Puerto Rico), Canada (except Quebec), Australia, New Zealand, South Africa, India, Singapore, and many other generally English-speaking countries or Commonwealth countries. Basically, every country which has been colonised at some time by Britain except those British colonies that were taken over from other Empires, such as Quebec (following French law to some extent) and South Africa (following Roman Dutch law to some extent) where the prior civil law system was retained to respect the civil rights of the local colonists. India's system of common law is also a mixture of English law and the local Hindu law[?].
The main alternative to the common law system is the civil law system, which is used in Continental Europe, Quebec, Louisiana, the former Soviet bloc, and most of the rest of the world. Scotland is often said to use the civil law but in fact it has a unique system which combines elements of an uncodified civil law dating back to the Corpus Juris Civilis with a influence of common law after the unification with England in 1707.
Statutes which reflect English common law are understood to always be interpreted in light of the common law tradition, and so may leave a number of things unsaid because they are already understood from pre-existing case law and custom.
By contrast, some laws are purely statutory, and may create a new cause of action. An example of this would be the tort of wrongful death[?], which allows certain persons, usually a spouse or child or estate, to sue for damages on behalf of the deceased. There is no such tort in English common law; thus, any state that lacks a wrongful death statute will not allow a lawsuit for the wrongful death of a loved one. Where a wrongful death statute exists, the damages or compensation available are limited to those outlined in the statute (typically, an upper limit on the amount of damages). Courts generally interpret statutes that create new causes of action narrowly - that is, limited to their precise terms - because the courts recognize the legistature as being supreme in decided the reach of judge made law unless such statute should violate some second order constitutional law provision.
Where a tort is grounded in common law, then all damages traditionally recognized historically for that tort may be sued for, whether mentioned in current statutory law or not. For instance, a person who sustains bodily injury through the negligence of another may sue for medical costs, pain, suffering, loss of earnings or earning capacity, mental and/or emotional distress, loss of quality of life, disfigurement, and more. These damages need not be set forth in statute as they already exist in the tradition of common law. However, without a wrongful death statute, most of them are extinguished upon death. An old saw (in states with no or low wrongful death damages) stated that it was better to back up and over the person to ensure his death and limit your exposure!
The definitive historical treatise on the common law is Commentaries on the Laws of England, written by Sir William Blackstone and first published in 1765 - 1769. Since 1979 a facsimile edition of that first edition has been available in four paper-bound volumes. Today it has been superseded in the English part of the United Kingdom by Halsbury's Laws of England that covers both common and stautory English law.