Traditional contract law developed rules and principles controlling the voluntary assumption of obligations, regulating the performance of obligations so assumed, and providing sanctions for failure to perform.

Some of the rules respecting offer and acceptance are designed to operate only when a contrary intention has not been indicated. Thus, in German law an offer cannot be withdrawn by an offeror until the time stipulated in the offer or, if no time is stipulated, until a reasonable time has passed, but this rule yields to a statement in the offer to the effect that it shall be revocable. In Anglo-American common law, when parties contract by correspondence, the acceptance takes place on dispatch of the letter, but the offeror can stipulate that no contract will be formed until the acceptance has been received. These rules serve to fill in points on which the parties in their negotiations have not, for one reason or another, been specific.

Another function of rules relating to offer and acceptance is to enable the parties to understand and to mark when their discussions pass from an exploratory stage to the stage of commitment. The concepts of offer and acceptance are somewhat formal; they assume that the negotiations pass through clearly distinguishable phases, which is often not the case. But they help the parties to distinguish negotiation from commitment. The two words offer and acceptance become firmly associated with the assumption of obligations.

Different legal systems frequently advance comparable policies in quite different ways. Several distinctly different patterns are found in the approach of modern legal systems to the problems of whether an offeror is free to revoke an offer before acceptance and of when an acceptance is effective to form a contract. Perhaps the polar extremes are represented by German civil law on one hand and Anglo-American common law on the other. In the German view, an offer binds the offeror for any stipulated period or, when the offer is silent as to time, for a reasonable period unless the offeror has expressly made the offer revocable. The common-law rule is the opposite: an offer is revocable until it has been accepted. The two systems also have sharply divergent rules with respect to the point at which, when the parties are contracting by correspondence, the acceptance takes effect to conclude the contract. In German law the acceptance takes effect when it reaches the offeror, in the sense that the offeror either knows or can learn of it. In the common law, on the other hand, if the offeree uses an appropriate means of communication, the acceptance is effective on dispatch unless the offeror stipulated the contrary in the offer. (A revocation by the offeror, however, does not take effect until received by the offeree.)

How are these divergencies in the rules respecting offer and acceptance to be explained? In particular, do they reflect fundamental policy differences or simply different techniques designed to forward quite similar purposes? An examination of a typical problem posed when parties contract by correspondence suggests the latter explanation. Upon receipt of an offer, offerees frequently change their position by, for example, refusing or ignoring other offers, neglecting to seek additional offers, or themselves making propositions based on the offer made to them. For this reason the legal system sees a need to provide offerees with a secure point of departure for their decision, in order both to protect them and to facilitate commerce generally. The German system provides this protection by making the offer in principle irrevocable. The common law, on the other hand, found this solution excluded by its doctrine of consideration; as the offeree does not give anything in exchange for the offer’s irrevocability, consideration is lacking to support an obligation not to revoke. (On the other hand, the Uniform Commercial Code, which has been adopted everywhere in the United States, provides that a firm offer made by a merchant is irrevocable even though the other party has given no consideration.) The common law is not entirely insensitive to the offeree’s predicament. The rule that the acceptance is effective upon dispatch creates a situation in which the offeror who wishes to revoke an offer is uncertain whether or not it can be revoked, since the revocation is not effective until receipt, whereas the offeree’s acceptance, if one is made, takes effect on dispatch. This uncertainty makes the consequences of an attempted revocation unpredictable and thereby inhibits an offeror who might otherwise seek to revoke. In sum, the German and Anglo-American systems both try to achieve, and in a measure succeed in achieving, a fair balance between the offeror and the offeree.

In all systems of contract law, certain classes of transactions are treated as unenforceable by the judicial process because they are thought to involve unusual hazards for a contracting party or to be of marginal social utility. There are, in both civil-law and common-law systems, four kinds of concern that lead the systems to treat certain types of transaction as unenforceable. These four kinds of concern may be called evidentiary, cautionary, channeling, and deterrent. The evidentiary concern springs from the desire to protect both the individual citizen and the courts against manufactured evidence and insufficient proof. The cautionary concern seeks to safeguard individuals against both their own rashness and the importuning of others. The channeling concern seeks to mark off or label obligations that may be enforceable and to direct attention to the problem of the extent and kind of the legal obligation, so that individuals will know the legal significance that their actions may have. Finally, the deterrent concern refers to those types of transaction that are discouraged because they are felt to be of doubtful value to society.

Two quite different techniques are used to delineate types of transaction that are unenforceable in their natural, or normal, state. The first proceeds by describing the type in functional or economic terms. The common-law Statute of Frauds enacted by the English Parliament in 1677 provided that the following six kinds of contracts should be unenforceable unless expressed in writing: contracts to sell goods exceeding a certain value; contracts to sell any interest in land; agreements that are not to be performed within a year of their making; agreements upon consideration of marriage; suretyship agreements; and undertakings by an executor or administrator to be surety on a debt of the deceased for which the estate is liable. Civil-law systems typically describe as unenforceable in the absence of an appropriate formality noncommercial contractual obligations exceeding a certain value; mortgages created by contract; noncommercial compromise agreements; marriage contracts; agreements binding a party to transfer all, or a fractional part of, its property; leases to run for more than one year; assumptions of the obligation to stand as surety, at least when the operation is not a commercial one on the surety’s part; promise of an annuity; and promises to make gifts.

Another less direct technique for delineating unenforceable types of transaction derives from the common law’s doctrine of consideration. It holds transactions unenforceable in the absence of a bargained-for exchange. This class would include, for example, promises to make gifts. The approach tends to be too all-embracing, treating certain types of transaction as suspect when there is little or no practical justification for doing so. It is not clearly demonstrated, for example, that an option agreement made by two businessmen should be handled differently from many other kinds of commercial dealings. A strong argument exists that the common law’s handling of commercial options, business compromises, and other business transactions lacking an element of exchange is more a logical deduction from the general doctrine of consideration than an expression of justifiable policy concerns.

Except in cases where the ground for unenforceability is radical, when a given transaction type is considered unenforceable the legal system should prescribe an extrinsic element the addition of which will cure the defect—for example, expressing the agreement in writing, performing it in part, or having a document drawn up with the participation of a legally qualified notary or other public official who holds a special appointment from the state and is charged with handling and recording various types of transactions.

A complex situation has arisen with respect to the two most generally available extrinsic elements, the seal and the payment of a nominal consideration. Various states of the United States no longer consider the seal as an effective extrinsic element. The seal’s decline is rooted in its changed significance in the modern, literate, democratic world. The seal was originally an impression, usually in wax, of a device, or design, representing an individual or a family. In modern times, the courts, with legislative assistance in a fair number of the states of the United States, have recognized easy-going substitutes for the wax seal, such as simple writing presumed to have been made for sufficient consideration or, in special circumstances, parol (oral) agreement for valid consideration. The effect has been to render the seal progressively less effective, particularly from the cautionary perspective, and many courts now refuse to accept it as a satisfactory formality.

Nominal consideration is a subtle and ingenious formality. Its essence is the introduction of a contrived element of exchange into the transaction. Thus A, desiring to be bound to give B $10,000, requests B to promise to give (or to give) A a peppercorn in exchange. B’s promise (or performance) is an element, extrinsic to a normal gift promise, introduced by the parties in an effort to render the transaction enforceable (since the law does not treat normal gift promises as enforceable). Common-law courts often accept nominal consideration when used in a business context, such as in an option arrangement or a compromise agreement; its effectiveness is understandably more doubtful in the context of a gift promise, since such a transaction involves greater dangers for one party and is socially more marginal.

Civil-law systems have less need than the common law for a formality such as nominal consideration; they prescribe methods directly in their statutes. Interestingly enough, however, in some civil-law systems an analogous, judicially developed formality has emerged—the disguised donation (donation déguisée) of French law, in which the parties cast a gift promise in the form of an onerous transaction, such as a sale. It can be argued that both the nominal considerations and the disguised donation serve at least the cautionary and channeling functions of formalities mentioned above.

Another kind of extrinsic element recognized by some courts, especially in the common-law countries, is one party’s reliance upon the promise of the other. The fact of reliance argues in favour of enforcement because it indicates that an underlying understanding existed between the parties and because the relying party may suffer as a consequence of its change of position. Some courts will enforce initially suspect transactions when several extrinsic elements are present in combination. A common-law court, for example, may enforce a gift promise in which the element of reliance was present in addition to a seal or a nominal consideration. Other extrinsic elements, either alone or in combination with reliance, a seal, or a nominal consideration, may also render a transaction enforceable. Cases, for example, in which the promisor dies without attempting to revoke a gift promise could be enforced, as distinguished from cases in which the promisor seeks to revoke.