Acceptance: Mirror Rule

Under common law, acceptance must mirror the offer; additional or different terms are counteroffers.

Representative cases

• Nelson v. Estate of Campbell 2023 S.D. 14 · South Dakota Supreme Court
• Nelson v. Estate of Campbell 2023 S.D. 14 · South Dakota Supreme Court
• Nicole Lampo v. Amedisys Holding, LLC Supreme Court of South Carolina

Related Formation rules

• Contract DefinedA contract is a legally enforceable promise formed by mutual assent and consideration.
• Offer RequirementsAn offer is a manifestation of intent to be bound with definite terms communicated to an identifiable offeree.
• Termination of OfferOffers terminate by revocation, rejection, lapse, death, or destruction of subject matter.
• Option ContractsAn option is irrevocable when supported by consideration for a promise to keep the offer open.
• Firm Offers (UCC)A merchant’s signed writing assuring it will remain open is irrevocable for the period stated, up to 3 months.
• Acceptance by PerformanceUnilateral contracts are accepted only by complete performance.
• Acceptance by PromiseBilateral contracts are accepted by a return promise or beginning performance.
• Mailbox RuleAcceptance is effective upon dispatch unless otherwise specified.

Part of Contracts on Core Legal Rules — foundational MBE-tested principles with primary-source citations.