Question: What is the basis of English Common law?
About the article "Hong Kong", section "Legal system and judiciary".

Candidate passages:
English law is the legal system of England and Wales.
Due to the British Empire, it has been exported across the world: it is the basis of common law jurisprudence of most Commonwealth countries, and English law prior to the American revolution is still part of the law of the United States, except in Louisiana, and provides the basis for many American legal traditions and policies, though it has no superseding jurisdiction. 
British Virgin Islands tort law is almost entirely based upon English common law. 
Medieval Roman law is the continuation and development of ancient Roman law that developed in the European Late Middle Ages.
Based on the ancient text of Roman law, the Corpus iuris civilis, it added many new concepts, and formed the basis of the later civil law systems that prevail in most countries today outside the common law countries of the English-speaking world. 
There are two established approaches to this issue.
Traditionally, common law systems such as those of England and the United States have proceeded on the basis of what may be termed the "unjust factor" approach.
Traditionally, civil law systems such as those of France and Germany have proceeded on the basis of what may be termed the "absence of basis" approach.
More recently, many common law systems have showed signs of a possible move towards the "absence of basis" approach (see for example the law of North Dakota in the section on the United States below).
Both approaches will be discussed.
The "unjust factors" approach requires the claimant to point to one of a number of factors recognized by the law as rendering the defendant's enrichment unjust.
English law clearly recognises at least the following unjust factors:  Mistake of fact  Mistake of law  Duress  Undue influence  Total failure of consideration  Miscellaneous policy-based unjust factors such as "withdrawal within the "locus poenitentiae"" It is at least arguable that English law also recognizes the following unjust factors, but some controversy surrounds each:  Ignorance/powerlessness  Unconscionability  Partial failure of consideration  Absence of consideration "Absence of consideration" is particularly controversial because the cases that support its existence as an unjust factor can also be used to support the view that English law has begun to favour the "absence of basis" approach.
The "absence of basis" approach does not deal in individual unjust factors.
Instead it seeks to identify enrichments with no legitimate explanatory basis.
Example: Imagine that A contracts with B that A will pay $150 up front for B to clean his house.
A pays the money, and B's enrichment has a legitimate explanatory basis - he was paid under a valid contract.
However, let us now change the example and assume that the contract was in fact void.
This is discovered after A has paid the money, but before B cleans the house.
B"'"s enrichment no longer has a legitimate explanatory basis, so B must repay the $150 to A.
Notice that in the example just given, exactly the same conclusion would be reached using the "unjust factors" approach.
Under that approach, A would not be able to point to an unjust factor provided that the contract was valid, but could point to the unjust factor of total failure of consideration once we assume that it was void.
In the vast majority of cases, a properly developed "unjust factors" approach and a properly developed "absence of basis" approach will reach the same result. 
Ancient China and ancient India had historically independent schools of legal theory and practice such as the "Laws of Manu" or the "Arthashastra" in India and traditional Chinese law in China.
Because Germany was a rising power in the late 19th century, and codified civil law is more 'exportable' than large bodies of common law jurisprudence, the German Civil Code has been highly influential for most oriental legal systems, and forms the basis of civil law in Japan and South Korea.
In China, the German Civil Code was introduced in the later years of the Qing Dynasty and formed the basis of the law of the Republic of China which remains in force in Taiwan.
The current legal infrastructure in the People's Republic of China reflects influences from the German-based civil law, English-based common law in Hong Kong, Soviet-influenced Socialist law, United States-style banking and securities law, and traditional Chinese law.
In India, and other previous members of the Commonwealth, English common law forms the basis of private law.