Mirror Image Rule

Also known as: Acceptance Must Mirror Offer

In one sentence

The principle that an acceptance must match the offer exactly, or it becomes a counteroffer instead.

Plain English

Under the mirror image rule, when someone makes you an offer, your acceptance must be identical to what they proposed. If you accept but change any terms—even small ones—you're not really accepting; you're making a counteroffer. This rule comes from old contract law and can create problems in real business deals where parties often tweak terms back and forth. The UCC has softened this rule for sales of goods, allowing some flexibility in commercial transactions.

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Example

A seller offers to sell 100 widgets for $5 each, delivery in 30 days. The buyer responds "I accept, but I need delivery in 15 days." Because the buyer changed the delivery term, this is not an acceptance under the mirror image rule—it's a counteroffer that the seller can accept or reject.

Used in a sentence

“The mirror image rule meant that the buyer's acceptance, which added a warranty not in the original offer, created a counteroffer rather than a binding contract.”

Related terms

Mutual Assent

Both parties agree to the same contract terms at the same time.

Offeror

The person who makes an offer to enter into a contract.

Unilateral Offer

An offer that invites acceptance by performance of an act, rather than by a return promise.

Legal Value

Something of worth in the eyes of the law that can support a binding contract.

Capacity

The legal and mental ability to enter into a binding contract.

Good Faith and Fair Dealing

A legal duty to act honestly and fairly when making and performing contracts.

Offer

A proposal to enter into a binding agreement on specific terms.

Acceptance

Agreeing to the exact terms of an offer, creating a binding contract.

This page is a plain-English reference and is not legal advice. Laws vary by jurisdiction and change over time. For specific situations consult a licensed attorney.