Manifestation of mutual assent to an exchange requires that each party either make a promise or begin or render a performance.
a. Manifestation of assent. Assent to the formation of an informal contract is operative only to the extent that it is manifested. Compare § 3 and Comment b to § 2. As to the manifestation of assent by conduct other than words, see §§ 4 and 19. Rules for cases where one party could reasonably draw more than one inference as to the intention of another are stated in the following sections, in connection with the scope of contractual obligations (see §§ 201, 219), and in connection with mistake (see § 151-58).
b. Assent by promise or performance. Where a bargain has been fully performed on one side, there is commonly no need to determine the moment of making of the contract or whether the performing party made a promise before he performed. Those issues ordinarily become important only when a dispute arises at an earlier stage. In the typical case such a dispute involves an exchange of promises before any performance takes place; there is an offer containing a promise and made binding by an acceptance containing a return promise. Section 50. The beginning or tender of performance may operate as such a return promise under § 63. In less common cases, acceptance may be made by a performance under § 54, and the beginning of performance may have an intermediate effect of making the offer irrevocable under § 45.
c. Sham or jest. Where all the parties to what would otherwise be a bargain manifest an intention that the transaction is not to be taken seriously, there is no such manifestation of assent to the exchange as is required by this Section. In some cases the setting makes it clear that there is no contract, as where a business transaction is simulated on a stage during a dramatic performance. In other cases, there may be doubt as to whether there is a joke, or one of the parties may take the joke seriously. If one party is deceived and has no reason to know of the joke the law takes the joker at his word. Even if the deceived party had reason to know of the joke, there may be a claim for fraud or unjust enrichment by virtue of the promise made. Where the parties to a sham transaction intend to deceive third parties, considerations of public policy may sometimes preclude a defense of sham. Cf. Illustration 1 to § 21.