Mirror Image Rule

The mirror image rule is a common law principle requiring that an acceptance correspond precisely to the terms of the offer. If the purported acceptance changes, adds, or omits any term of the offer, it is not an acceptance at all but rather a counteroffer, which terminates the original offer and creates a new offer that the original offeror may accept or reject.

The rule reflects the strict contractual principle that mutual assent requires agreement on the same terms. If A offers to sell a car for $10,000 and B responds "I accept, but the price should be $9,500," B has not accepted A's offer but has made a counteroffer. A's original offer is terminated and cannot be accepted by B.

The UCC significantly relaxes the mirror image rule for sales of goods through Section 2-207 (the "battle of the forms" provision). Under the UCC, a definite and seasonable expression of acceptance operates as an acceptance even if it contains additional or different terms. Between merchants, additional terms become part of the contract unless they materially alter the offer, the offer expressly limits acceptance to its terms, or the offeror objects within a reasonable time. This approach reflects the commercial reality that businesses routinely exchange forms with different boilerplate terms.

The tension between the common law mirror image rule and UCC Section 2-207 is one of the most tested areas of contracts law. Students must know which applies based on whether the transaction involves goods (UCC) or services/other subject matter (common law).

On exams, mirror image rule issues arise whenever the offeree's response does not perfectly match the offer. The analysis should identify whether the response is an acceptance with varying terms (UCC) or a counteroffer (common law), and what legal consequences follow.