Legal Definitions - Mirror Image Rule

The Mirror Image Rule is a principle in contract law stating that for a valid contract to be formed, an acceptance of an offer must precisely and unconditionally match the terms of the original offer. In other words, the acceptance must be a "mirror image" of the offer, reflecting all its terms without any changes, additions, or deletions. If the acceptance introduces new terms or modifies existing ones, it is generally considered a rejection of the original offer and becomes a counteroffer instead, preventing the formation of a contract under the initial terms.

Historically, this rule was applied very strictly. However, in modern commercial transactions, particularly for the sale of goods governed by the Uniform Commercial Code (UCC), the rule has been relaxed. A contract for goods may still be formed even if the acceptance contains minor additional or different terms, provided the core agreement remains intact and the new terms do not materially alter the offer.

• Example 1 (Strict Application - Common Law): A homeowner offers to sell their unique antique grandfather clock for $5,000. A potential buyer responds, "I accept your offer for the clock at $5,000, but only if you also include the matching antique stool."
  This scenario illustrates the strict Mirror Image Rule. The buyer's response is not an unconditional acceptance because it introduces a new term (the matching stool). Under common law, this would be considered a counteroffer, not an acceptance, and no contract for the clock alone would be formed based on the original offer.
• Example 2 (Strict Application - Common Law): A landlord offers to lease a commercial office space for $2,500 per month for a period of two years. A prospective tenant replies, "I agree to rent the office space for $2,500 per month, but I only want a 12-month lease."
  Here, the tenant's acceptance changes a material term of the offer – the duration of the lease. Because the acceptance does not perfectly mirror the offer's terms, it acts as a counteroffer rather than an acceptance. Therefore, no binding lease agreement is formed based on the landlord's original two-year offer.
• Example 3 (Relaxed Application - Modern Commercial Law for Goods): A restaurant owner sends a purchase order to a food supplier for 100 pounds of a specific type of coffee beans at a stated price. The supplier sends back an acknowledgment form confirming the quantity and price, but also includes a standard clause stating that "payment is due within 30 days of delivery."
  In this situation, which involves the sale of goods, modern contract law (like the UCC) might recognize a binding contract. Even though the supplier's acceptance added a term about payment, it is likely considered a minor, standard industry practice that does not fundamentally alter the core agreement (quantity, type, and price of coffee beans). Unless the restaurant owner specifically objects to this new term, a contract could still be formed.