mirror image rule

a rule governing contract formation that requires the acceptance of an offer match the offer in its terms, exactly and without variation of any kind. According to the mirror image rule, any variation in terms, between the acceptance and the offer, negates the acceptance and voids the agreement. The mirror image rule comes from English common law and still applies today except for merchant-to-merchant agreements which are subject to the rules of the Uniform Commercial Code (UCC). In effect, the variation of terms in an acceptance constitutes a counter offer, thus reversing the roles of the parties: the party originally making the offer (offeror) now becomes the party receiving the offer (offeree) and visa versa.

Ogden and Agnes want to build a swimming pool in their yard. A local contractor presents the couple with a written bid that lists the specifications for the pool such as length, width and depth. It also includes a description of the materials to be used, a tentative schedule for the project and the price. Thinking the price is a little high, Ogden crosses out the price written by the contractor, enters one he feels is more reasonable and signs the contract. According to the mirror image rule, no contract exists because the terms of the acceptance differed from the terms of the offer.