An error is a misunderstanding of one or more parties and can be invoked as a reason for the invalidity of the agreement. The Common Law has identified three types of errors in the treaty: frequent errors, reciprocal errors and unilateral errors. The Common Law describes the circumstances in which the law recognizes the existence of rights, privileges or powers arising from a promise. While trade and exchange rules pre-existed since ancient times, modern contract laws in the West have been understandable since the Industrial Revolution (from 1750), when more and more people worked in factories for a cash wage. In particular, the growing strength of the British economy and the adaptability and flexibility of English common law have led to a rapid evolution of English contract law. The colonies of the British Empire (including the United States and the Dominions) would take over metropolitan law. In the twentieth century, the growth of export trade led countries to adopt international agreements such as the Hague Visby Rules and the United Nations Convention on International Purchase Contracts in order to promote uniform rules. Each contracting party must be a “competent person” who is legitimate. The parties may be natural persons (“individuals”) or legal persons (“limited communities”). An agreement is reached when an “offer” is accepted.
The parties must intend to be legally bound; and, to be valid, the agreement must have both an appropriate “form” and a legitimate purpose. In England (and in jurisdictions that apply English contractual principles), parties must also exchange “considerations” to create “reciprocity of engagement,” as in simpkins v Country.  According to the common law, the elements of a contract; Offer, acceptance, intention to create legal relationships, to take into account and legality of the form and content. In colonial times, the concept of consideration was exported to many common law countries, but it is unknown in Scotland and civil courts.  Roman legal systems do not require or recognize any consideration, and some commentators have proposed abandoning the counterpart and replacing it as the basis for treaties.  However, legislation, not the development of justice, has been presented as the only way to eliminate this entrenched doctrine from the common law. Lord Justice Denning said: “The doctrine of consideration is too well entrenched to be overturned by a side wind.”  In the United States, the focus has been on the negotiation process, as hamer v. Sidway (1891) shows. As a general rule, contracts are oral or written, but written contracts have generally been preferred in common legal systems;  In 1677, England passed the Fraud Act which influenced similar fraud laws in the United States and other countries such as Australia.  In general, the Uniform Commercial Code, as adopted in the United States, requires a written contract for physical sales of products over 500 $US, and real estate contracts must be in writing.
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