A contract requires the agreement of the parties. Evidence of that agreement is an offer by one party and acceptance of that offer by the other. The offeror must be willing to trade otherwise it is an invitation to treat. The offeree must know of the offer and it must be fully accepted. For example, if the offeree responds with a request for further information, or a counter offer, then the offer has not been accepted. An offer can be accepted by conduct or by post according to the postal rule. The offer can be revoked at any time by the offeror before the offer is accepted or it may lapse after a reasonable time.

A social arrangement cannot become a contract as the parties do not intend to enter into a legal arrangement. For example, an agreement by one spouse to pay the other housekeeping money.

For the sale of land, there is an agreement between the parties when the buyer offers to buy at a certain price and the seller accepts that offer. NB there is no contract until exchange