Battle of the Forms: UCC 2-207, Knockout Rule, and Last Shot

In a battle of the forms, whose terms govern depends on UCC Section 2-207: a contract usually forms even when the buyer’s and seller’s paperwork disagrees, and courts then either strike the conflicting terms and fill the gaps with UCC defaults or, under an older approach still used in some jurisdictions, enforce whichever form was sent last before performance began. Which path a court takes, and which terms survive, turns on whether both parties are merchants, whether the added language materially alters the deal, and what the parties actually did after the forms crossed.

Why the Forms Conflict in the First Place

Most commercial deals don’t start with a single negotiated contract. A buyer sends a purchase order with standard terms on the back. The seller responds with an acknowledgment or invoice carrying its own boilerplate. Those forms routinely disagree on warranty coverage, delivery, limitation of liability, and dispute resolution. Neither side reads the other’s fine print, and the goods ship anyway.

The mismatches sit dormant until something goes wrong. A buyer’s form might promise a full refund for defective goods while the seller’s form limits the remedy to repair or replacement. A seller’s form might include an arbitration clause the buyer never agreed to. Both sides believe they have a deal. The documents tell two different stories about what that deal actually includes.

What UCC 2-207 Does

Section 2-207 starts from a simple premise. A response that clearly signals acceptance can still be an acceptance even if it introduces terms that differ from or add to the original offer. The contract forms at that moment, not later when someone performs.¹

There’s one major carve-out. If the acceptance is expressly conditional on the other party agreeing to the new or different terms, it doesn’t operate as an acceptance at all. It functions as a counteroffer, and no contract forms from the writings themselves.

When the writings don’t form a contract but both parties perform anyway, Section 2-207(3) takes over. The contract then consists of whatever terms the two forms actually agree on, plus default rules pulled from the rest of the UCC to fill the gaps.¹

Whether Both Sides Are Merchants Changes the Outcome

The UCC treats a merchant as someone who regularly deals in goods of the kind involved, or who holds themselves out as having specialized knowledge about the goods or trade practices.² That status matters because it changes what happens to additional terms in an acceptance.

When both parties are merchants, additional terms automatically become part of the contract unless one of three things is true:

The offer expressly limits acceptance to its own terms. Language like “acceptance is limited to the terms stated here” keeps additions out.
The additional term would materially alter the deal by significantly shifting risk, liability, or obligations.
The offeror objects within a reasonable time after seeing the new language.¹

When one or both parties are not merchants, additional terms are only proposals. They don’t become part of the contract unless the offeror affirmatively agrees to them.¹ A consumer buying from a business, for example, isn’t bound by terms tucked into a seller’s confirmation form absent actual agreement.

The Knockout Rule vs. the Last Shot Doctrine

Terms that directly conflict, rather than merely add something new, get treated differently. Courts have taken two approaches.

The knockout rule, which most courts now follow, throws out any terms where the two forms disagree. If the buyer’s form sends disputes to court and the seller’s sends them to arbitration, neither term survives. The contract keeps only what both forms have in common, and UCC defaults fill in everything else. The reasoning tracks Section 2-207(3): where writings conflict, the deal consists of what the parties agreed on plus supplementary UCC rules.¹

The last shot doctrine is the older common law approach. It gives control to whichever form was sent last before performance began, reasoning that the other party accepted those terms by proceeding. The problem is obvious. It rewards whoever fires off the final piece of paper, regardless of whether the other side read or agreed to it. Courts have increasingly moved away from this approach because it produces the arbitrary results that Section 2-207 was written to prevent, but it still surfaces in some jurisdictions and in cases involving pure counteroffers.

What the UCC Fills In When Terms Get Knocked Out

When the knockout rule eliminates conflicting terms, the UCC doesn’t leave a vacuum. It supplies defaults for the most common provisions, and those defaults decide what actually governs the deal:

Price. If conflicting price terms cancel each other, the UCC supplies a reasonable price at the time of delivery.³
Delivery location. Without an agreed pickup point, the goods are to be picked up at the seller’s place of business.⁴
Delivery timing. With no time specified, delivery must occur within a reasonable time.⁵
Warranty. If conflicting warranty terms fall out, the implied warranty of merchantability applies. The goods must be fit for their ordinary purpose, pass without objection in the trade, and conform to any labeling.⁶

These defaults tend to favor buyers. A seller who loses a limitation-of-liability clause ends up subject to the full implied warranty of merchantability with no cap on damages. A seller who loses its delivery terms has to make goods available at its own location instead of shifting shipping to the buyer. Sellers in particular have strong reason to resolve conflicts before performance rather than accept what the UCC fills in.

When an Added Term Counts as a “Material Alteration”

Between merchants, a term that materially alters the deal cannot become part of the contract without explicit consent. Courts ask whether the term would cause surprise or hardship if slipped in without the other party’s awareness.

In Dorton v. Collins & Aikman Corp., the Sixth Circuit examined whether an arbitration clause added to a seller’s acknowledgment form materially altered the buyer’s original oral offer. The court sent the question back for further fact-finding but held that if the clause did materially alter the deal, the buyer could not be bound absent express agreement.⁷

The pattern is consistent. Clauses that restrict where and how disputes get resolved, disclaim warranties, or cap liability are the ones most often found material. Terms that wouldn’t surprise a reasonable merchant in the trade, like an industry-standard inspection period, generally aren’t. The more a term shifts risk onto the other side, the less likely it survives.

How Performance and Prior Dealings Can Lock Terms In

When the paperwork is a mess, courts look at what the parties actually did. Mutual performance can establish that a contract exists even where the exchanged writings can’t be reconciled. In Ionics, Inc. v. Elmwood Sensors, Inc., the First Circuit emphasized that going ahead with the deal can indicate acceptance of a contract’s existence, even when the documents contain irreconcilable terms.⁸

Prior dealings and industry customs matter too. If you’ve done twenty transactions with the same counterparty and never objected to a particular term on their form, a court may treat that history as acceptance. If a term reflects standard trade practice, courts are more willing to treat it as part of the deal. Silence plus continued performance can become consent, which makes it risky to ignore language you disagree with and hope it goes away.

Cross-Border Sales Follow Different Rules

If your transaction crosses international borders, the United Nations Convention on Contracts for the International Sale of Goods (CISG) may apply instead of the UCC, and it handles conflicts very differently. Under CISG Article 19, a response that adds or changes terms is generally treated as a rejection and counteroffer, not an acceptance.⁹ That’s closer to the old mirror image rule than to the UCC’s flexible approach.

There’s a narrow exception for non-material changes: if the additions don’t materially alter the offer and the offeror doesn’t promptly object, the acceptance stands with the modified terms included. But the CISG defines material alteration broadly. Any change touching price, payment, quality, quantity, delivery, liability, or dispute resolution counts.⁹ That covers virtually every term businesses fight over, so the exception rarely helps. Assuming 2-207 governs your foreign transactions is a mistake that can leave you bound to terms you didn’t expect.

How to Avoid Ending Up in the Fight

The cleanest fix is to skip the dueling forms and negotiate a single signed master agreement before any purchase orders start moving. That isn’t practical for every deal, but for ongoing relationships with real dollar volume it eliminates the problem at the source.

When standardized forms are unavoidable, a few drafting and workflow habits shift the odds:

Make your acceptance expressly conditional on the other party’s agreement to your terms. Under 2-207(1), that prevents their form from controlling by default.¹
State in your offer that acceptance is limited to the terms in your document. Between merchants, 2-207(2)(a) then blocks additional terms from sneaking in.
Object in writing, within a reasonable time, to any incoming terms you don’t want. Timely objection keeps them out under 2-207(2)(c).¹
Read the other side’s form before you perform. Shipping or accepting delivery without checking the boilerplate is how parties end up subject to UCC defaults neither of them wanted.

None of these steps guarantees the outcome you want. Each one moves the odds in your direction. The worst place to be is discovering the conflict only after a dispute has already started, when a judge will decide whose terms governed the deal you thought you already had.

1
Cornell Law School. UCC 2-207 – Additional Terms in Acceptance or Confirmation
2
Cornell Law School. UCC 2-104 – Definitions: Merchant; Between Merchants; Financing Agency
3
Cornell Law School. UCC 2-305 – Open Price Term
4
Cornell Law School. UCC 2-308 – Absence of Specified Place for Delivery
5
Cornell Law School. UCC 2-309 – Absence of Specific Time Provisions; Notice of Termination
6
Cornell Law School. UCC 2-314 – Implied Warranty: Merchantability; Usage of Trade
7
Justia. Dorton v. Collins and Aikman Corp., 453 F.2d 1161 (6th Cir. 1972)
8
Justia. Ionics, Inc. v. Elmwood Sensors, Inc., 110 F.3d 184 (1st Cir. 1997)
9
CISG-online.org. Art. 19 CISG