Laws grind the poor， and rich men rule the law.
—Oliver Goldsmith H （British writer）
著名法学家Roscoe Pound曾说：“社会秩序取决于行为的稳定性和可预见性，其中遵守承诺是一个大问题。”承诺是将来做什么或不做什么的保证，合同是“一个承诺或一组承诺，如果违反了该承诺，法律将给予救济；或者法律规定的必须履行的某种义务”。简而言之，合同是建立在承诺或相互承诺基础上的一种协议，可由法院强制执行。
美国是实行普通法制度的联邦制国家，美国的合同法制度是英国合同法制度的继承和发展，因而在合同法制度方面，既有成文法，也有案例法，但是主要的合同法规则还是由各州自己制定。从核心概念和基础理论方面而言，英美合同法有许多共通之处。
Introduction to Contract Law
English contract law is an influential body of law regulating the law of contract that operates in England and Wales. Its doctrines form the basis of contract law across the Commonwealth， including Australia， Canada， New Zealand contract law， India and South Africa， as well as the United States and the wider common law world. It also influences international law.
A contract is an exchange of promises between two or more parties to do， or refrain from doing， an act which is enforceable in a court of law. It is a binding legal agreement. That is to say， a contractis an exchange of promises for the breach of which the law will provide a remedy.
Agreement is said to be reached when an offer capable of immediate acceptance is met with a“mirror image”acceptance. The parties must have the necessary capacity to contract and the contract must not be trifling， indeterminate， impossible or illegal. Contract law is based on the principle expressed in the Latin phrase pacta sunt servanda（ usually translated“pacts must be kept”， but more literally“agreements are to be kept”） . Breach of contract is recognized by the law and remedies can be provided. Sometimes written contracts are required， such as when buying a house. However， most contracts can be and are made orally， such as purchasing a book or a sandwich. Contract law can be classified， as is habitual in civil law systems， as part of a general law of obligations （ along with tort， unjust enrichment or restitution） .
According to legal scholar Sir John William Salmond， a contract is“an agreement creating and defining the obligations between two or more parties”.
As a means of economic ordering， contract relies on the notion of consensual exchange and has been extensively discussed in broader economic， sociological and anthropological terms.
However， contract is a form of economic ordering common throughout the world， and different rules apply in jurisdictions applying civil law （ derived from Roman law principles） ， Islamic law， socialist legal systems， and customary or local law. The primacy of discussion of common law principles in writing about contract may derive from the primacy of these systems in international business. Common law jurisdictions usually offer proceedings in the English language， which has become to an extent the lingua franca of international business， tend to have much larger law firms than in civilian jurisdictions， able to satisfy clients that their range of legal needs can be met， and unlike civilian jurisdictions， judges in common law jurisdictions are generally senior lawyers of considerable practical experience.Another possible reason is that the common law retains a high degree of freedom of contract， with parties largely free to set their own terms， whereas civilian systems typically prescribe large parts of the contents of contracts for the parties， with no opt-out provision （ see， for example the French Civil Code） . It is very common for businesses not located in common law jurisdictions to opt in to the common law through“choice of law”clauses， with the most common jurisdictions of choice probably being England &；； Wales and New York.
In common law systems， the five key requirements for the creation of a contract are：①offer and acceptance （ agreement） ；②consideration；③an intention to create legal relations；④legal capacity；⑤formalities.
Offer and acceptance
The most important feature of a contract is that one party makes an offer for an arrangement that another accepts. This can be called a“concurrence of wills”or“ad idem”（ meeting of minds） of two or more parties. The concept is somewhat contested. The obvious objection is that a court cannot read minds and the existence or otherwise of agreement is judged objectively，with only limited room for questioning subjective intention （ see Smith vs. Hughes） . Richard Austen-Baker has suggested that the perpetuation of the idea of“meeting of minds”may come from a misunderstanding of the Latin term“consensus ad idem”， which actually means“agreement to the same thing”. There must be evidence that the parties had each from an objective perspective engaged in conduct manifesting their assent， and a contract will be formed when the parties have met such a requirement. An objective perspective means that it is only necessary that somebody gives the impression of offering or accepting contractual terms in the eyes of a reasonable person， notthatthey actually did want to form a contract.