Mirror Image Rule

@bob7947No, not in litigation, but it has come up in government contracting. See, e.g., Professional Management Consulting Services, LLC, ASBCA No. 61861, 20-1 BCA 37638, June 25, 2020.

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Contract formation is typically subject to the mirror image rule, and an acceptance containing additional or different terms is treated as a rejection of the offer and as a counter-offer. See, e.g., First Commerce Corp. v. United States, 335 F.3d 1373, 1381 (Fed. Cir. 2003). This is also referred to as the “last shot” rule.

You heard about it I'm sure in connection with Two Rivers Corporate Centre, LP, ---Fed.Cl.---, June 7, 2021.

See Black's Law Dictionary:

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mirror-image rule (1972) Contracts. The doctrine that the acceptance of a contractual offer must be positive, unconditional, unequivocal, and unambiguous, and must not change, add to, or qualify the terms of the offer; the common-law principle that for a contract to be formed, the terms of an acceptance must correspond exactly with those of the offer. • In modern commercial contexts, the mirror-image rule has been replaced by a UCC provision that allows parties to enforce their agreement despite minor discrepancies between the offer and the acceptance. The rule still applies to international sales contracts governed by the UN Convention on Contracts for the International Sales of Goods (article 19). — Also termed ribbon-matching rule. See BATTLE OF THE FORMS.

Cibinic and Nash discuss the principle without using the term in Formation of Government Contracts, 4th ed., pp.250-252, under the heading "Nonacceptance Responses to Offers."

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Under traditional contract law, an acceptance must unequivocally conform to the terms of the offer in order to create a binding  contractual agreement...

They cite the Restatement ,Second, Contracts § 58:

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An acceptance must comply with the requirements of the offer as to the promise to be made or the performance to be rendered.

According to Black's Law Dictionary the term "mirror image rule" dates only to 1972.

Thanks.  Yes, today was the first time I've seen that terminology and it is one of the cases on the Home Page.  Whoever reads this will now hear of it too.  I added a link to the opinion in your Two Rivers citation.