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Offer, acceptance, and invitation to treat

Contracts may be bilateral or unilateral. A bilateral contract is an agreement in which each of the parties to the contract makes a promise or set of promises to each other. For example, in a contract for the sale of a home, the buyer promises to pay the seller $200,000 in exchange for the seller's promise to deliver title to the property. Bilateral contracts commonly take place in the daily flow of commercial transactions. Less common are unilateral contracts, in which one party makes a promise, but the other side does not promise anything. In these cases, those accepting the offer are not required to communicate their acceptance to the offeror. In a reward contract, for example, a person who has lost a dog could promise a reward if the dog is found, through publication or orally. The payment could be additionally conditioned on the dog being returned alive. Those who learn of the reward are not required to search for the dog, but if someone finds the dog and delivers it, the promisor is required to pay. On the other hand, advertisements which promise bargains are generally regarded not as offers for unilateral contracts but merely "invitations to treat". Some have criticised the categorisation of contracts into bilateral and unilateral ones. For example, the High Court of Australia stated that the term unilateral contract is "unscientific and misleading".