A contract is an agreement in which each party assents to the terms of the other party. Without mutual assent there cannot be a contract, and this implies that the assent each person gives must be with reference to that of the other. If Toni places several alternative offers on the table, only one of which can be accepted, and invites Sandy to choose, no contract is formed if Sandy says merely, “I accept your terms.” Sandy must specify which offer she is assenting to.
From this general proposition, it follows that no contract can be legally binding unless an offer is in fact communicated to the offeree. If you write an e-mail to a friend with an offer to sell your car for a certain sum and then get distracted and forget to send it, no offer has been made. If your friend coincidentally e-mails you the following day and says that she wants to buy your car and names the same sum, no contract has been made. Her e-mail to you is not an acceptance, since she did not know of your offer; it is, instead, an offer or an invitation to make an offer. Nor would there have been a contract if you had sent your communication and the two e-mails crossed in cyberspace. Both e-mails would be offers, and for a valid contract to be formed, it would still be necessary for one of you to accept the other’s offer. An offer is not effective until it is received by the offeree (and that’s also true of a revocation of the offer, and a rejection of the offer by the offeree).
The requirement that an offer be communicated does not mean that every term must be communicated. You call up your friend and offer to sell him your car. You tell him the price and start to tell him that you will throw in the snow tires but will not pay for a new inspection, and that you expect to keep the car another three weeks. Impatiently, he cuts you off and says, “Never mind about all that; I’ll accept your offer on whatever terms you want.” You and he have a contract.
These principles apply to unknown offers of reward. An offer of a reward constitutes a unilateral contract that can be made binding only by performing the task for which the reward is offered. Suppose that Bonnie posts on a tree a sign offering a reward for returning her missing dog. If you saw the sign, found the dog, and returned it, you would have fulfilled the essentials of the offer. But if you chanced upon the dog, read the tag around its neck, and returned it without ever having been aware that a reward was offered, then you have not responded to the offer, even if you acted in the hope that the owner would reward you. There is no contractual obligation.
In many states, a different result follows from an offer of a reward by a governmental entity. Commonly, local ordinances provide that a standing reward of, say, $1,000 will be paid to anyone providing information that leads to the arrest and conviction of arsonists. To collect the reward, it is not necessary for a person who does furnish local authorities with such information to know that a reward ordinance exists. In contract terms, the standing reward is viewed as a means of setting a climate in which people will be encouraged to act in certain ways in the expectation that they will earn unknown rewards. It is also possible to view the claim to a reward as noncontractual; the right to receive it is guaranteed, instead, by the local ordinance.
Although a completed act called for by an unknown private offer does not give rise to a contract, partial performance usually does. Suppose Apex Bakery posts a notice offering a one-week bonus to all bakers who work at least six months in the kitchen. Charlene works two months before discovering the notice on the bulletin board. Her original ignorance of the offer will not defeat her claim to the bonus if she continues working, for the offer serves as an inducement to complete the performance called for.