The term “common law” originally derives from the 1150s and 1160s, when Henry II of England established the secular English tribunals. The “common law” was the law that emerged as “common” throughout the realm (as distinct from the various legal codes that preceded it, such as Mercian law, the Danelaw and the law of Wessex) as the king’s judges followed each other’s decisions to create a unified common law throughout England. The doctrine of precedent developed during the 12th and 13th centuries, as the collective judicial decisions that were based in tradition, custom and precedent. 45] Common law, also known as case law or precedent, is law developed by judges through decisions of courts and similar tribunals, as opposed to statutes adopted through the legislative process orregulations issued by the executive branch.  Judge-made common law operated as the primary source of law for several hundred years, before Parliament acquired legislative powers to create statutory law. It is important to understand that common law is the older and more traditional source of law, and legislative power is simply a layer applied on top of the older common law foundation.
Since the 12th century, courts have had parallel and co-equal authority to make law — “legislating from the bench” is a traditional and essential function of courts, In a common law jurisdiction several stages of research and analysis are required to determine “what the law is” in a given situation. First, one must ascertain the facts. Then, one must locate any relevant statutes and cases. Then one must extract the principles, analogies and statements by various courts of what they consider important to determine how the next court is likely to rule on the facts of the present case.
Later decisions, and decisions of higher courts or legislatures carry more weight than earlier cases and those of lower courts.  Finally, one integrates all the lines drawn and reasons given, and determines “what the law is”. Then, one applies that law to the facts. The common law is more malleable than statutory law. First, common law courts are not absolutely bound by precedent, but can (when extraordinarily good reason is shown) reinterpret and revise the law, without legislative intervention, to adapt to new trends in political, legal and social philosophy.
Second, the common law evolves through a series of gradual steps, that gradually works out all the details, so that over a decade or more, the law can change substantially but without a sharp break, thereby reducing disruptive effects.  In contrast to common law incrementalism, the legislative process is very difficult to get started, as legislatures tend to delay action until a situation is totally intolerable. citation needed] For these reasons, legislative changes tend to be large, jarring and disruptive (sometimes positively, sometimes negatively, and sometimes with unintended consequences). Common law systems place great weight on court decisions, which are considered “law” with the same force of law as statutes—for nearly a millennium, common law courts have had the authority to make law where no legislative statute exists, and statutes mean what courts interpret them to mean.
By contrast, in civil law jurisdictions (the legal tradition that prevails, or is combined with common law, in Europe and most non-Islamic, non-common law countries), courts lack authority to act where there is no statute, and judicial precedent is given less interpretive weight (which means that a judge deciding a given case has more freedom to interpret the text of a statute independently, and less predictably), and scholarly literature is given more.
For example, the Napoleonic code expressly forbade French judges to pronounce general principles of law.  In common law legal systems (connotation 2), the common law (connotation 1) is crucial to understanding almost all important areas of law. For example, in England and Wales and in most states of theUnited States, the basic law of contracts, torts and property do not exist in statute, but only in common law In almost all areas of the law (even those where there is a statutory framework, such as contracts for the sale of goods, or the criminal aw), legislature-enacted statutes generally give only terse statements of general principle, and the fine boundaries and definitions exist only in the common law (connotation 1 The reliance on judicial opinion is a strength of common law systems, and is a significant contributor to the robust commercial systems in the United Kingdom and United States. Because there is reasonably precise guidance on almost every issue, parties (especially commercial parties) can predict whether a proposed course of action is likely to be lawful or unlawful.
This ability to predict gives more freedom to come close to the boundaries of the law.  For example, many commercial contracts are more economically efficient, and create greater wealth, because the parties know ahead of time that the proposed arrangement, though perhaps close to the line, is almost certainly legal. Newspapers, taxpayer-funded entities with some religious affiliation, and political parties can obtain fairly clear guidance on the boundaries within which their freedom of expression rights apply. Contract Law: Any agreement that is enforceable in courtis a contract.
Because a contract is a voluntary obligation, in contrast to paying compensation for a tort and restitution to reverse unjust enrichment, English law places a high value on ensuring people have truly consented to the deals that bind them in court. Generally a contract forms when one person makes an offer, and another person accepts it by communicating their assent or performing the offer’s terms. If the terms are certain, and the parties can be presumed from their behaviour to have intended that the terms are binding, generally the agreement is enforceable.
In principle, English law grants people broad freedom to agree the content of a deal. Terms in an agreement are incorporated through express promises, by reference to other terms or potentially through a course of dealing between two parties. Contract law works best when an agreement is performed, and recourse to the courts is never needed because each party knows her rights and duties. However, where an unforeseen event renders an agreement very hard, or even impossible to perform, the courts typically will construe the parties to want to have released themselves from their obligations.
It may also be that one party simply breaches a contract’s terms. If a contract is not substantially performed, then the innocent party is entitled to cease her own performance and sue for damages to put her in the position as if the contract were performed. -Although promises are made to be kept, parties to an agreement are generally free to determine how a contract is concluded, can be terminated and remedial consequences for breach of contract, just as they can generally determine a contract’s content.