In order to have a valid contract, the parties must have, and must communicate, a common intention. Their minds must meet in expressed agreement. If this element is absent, there can be no binding contract. For instance, in an English case the plaintiff agreed to sell and the defendants to buy a certain quality of Surat cotton to arrive by the ship "Peerless " from Bombay. The plaintiff offered cotton from a ship named "Peerless" from

Bombay, the defendants refused to accept it, and the plaintiff sued for damages for this alleged breach of contract. It was admitted that the defendants in using the term "Peerless" meant a different ship from that which the plaintiff had in mind, and in which the cotton actually arrived; it therefore appeared that there was no mutual consent to the same matter. Judgment was accordingly given for the defendants. On the other hand, the law looks to the expressions of the parties, and when their expressions necessarily indicate agreement, does not permit them to say that they were not agreed.

Consent is manifested by offer and acceptance. It follows from what has been said that both the offer and the acceptance must be communicated, but each may be communicated by conduct as well as by words. Thus if A asks X to work for him for certain wages, X in simply doing the work may accept the offer, unless some other form of acceptance was prescribed. It is also clear that the acceptance must be absolute, and in exact accordance with the terms of the offer. If A makes one offer, and X answers that he will do something a little different from what A suggested, there is no contract. X's reply may amount to a new offer, which A may subsequently accept. This principle will later be seen to be important in connection with an architect's submitting plans in response to a request for plans in competition.

An offer may by its terms remain open for a certain length of time; as for two weeks or until the return mail; if no duration is specified it can be accepted only within a reasonable time. What is a reasonable time depends upon the circumstances of each case. In an action of law, the question would be determined by the jury. An offer may be revoked at any time before acceptance. The revocation, however, must be communicated to the offeree. If A offers to furnish X with a cornice for a certain amount, A may, at any time before X has accepted the offer, effectively withdraw it by declaring to X his intention so to do. At the moment when a valid acceptance is made, the contract, if good in other respects, is complete, and both parties are bound. Acceptance is therefore irrevocable without the consent of both parties.

As to the important question when acceptance becomes binding - it is stated as a general rule that the acceptance is made when the acceptor has done all he can to communicate his inten-tion. Thus the mailing of a letter of acceptance properly stamped and addressed marks the making of a contract, and is irrevocable. Under this rule the delay or loss of the letter in the mail cannot delay or prevent the binding effect of the contract, so that it may happen that a person making an offer becomes bound without his knowledge. For this reason it is prudent to make it part of an offer that acceptance shall be only by letter delivered within a stated time at the office or into the hand of the person making the offer. Upon this point of acceptance by mail there has been some doubt about the law, and there are old decisions in one or two jurisdictions that there is no contract until the letter of acceptance is received. The rule about acceptance by telegram would probably be the same as that governing acceptance by letter. If, on the other hand, an acceptance were sent by an agent of the offeree, it would have to be delivered to be effective.

In this respect of the time of taking effect, revocation of an offer, which is ineffective until communicated, differs from acceptance.