Article 29 CISG and Section 2-209 UCC contain similar general principles on the modification of contract, whereby consideration is not required. Both also uphold formal requirements, but allow an exception where modification in ignorance of formal requirements or other conduct may operate as a waiver of, or preclude reliance on, formal requirements. Under Article 29 CISG, reliance on formal requirements is precluded where the other party has relied on the conduct. Under the UCC, the waiver applies regardless and can only be retracted where the other party has not materially changed its position in reliance on such waiver. The UCC also contains a separate provision for the statute of frauds.

(a) There was dispute as to whether there was an agreement to cancel the contract because the buyer had acquiesced in the agreement on the cancellation of the original agreement.

(b) The court concluded that in combination with other circumstances, silence may be interpreted as the acceptance of an offer of cancellation, which was the case here because the buyer refrained from further performance of the contract and did not exercise any contractual remedies.

(a) In attempting to modify a contract, the same concerns apply as when making counter-offers under Article 19 CISG. As the attempt to modify in the present case concerned the settlement of disputes by way of a forum selection clause, it was to be regarded as a material change which required specific acceptance from the offeree in order to constitute a valid modification of the existing contract.

(b) If you take this line of reasoning to its logical conclusion, then the risk exists that immaterial modifications proposed after the conclusion of a contract could become part of an existing contract if the offeree does not object to them without undue delay. 

(c) This cannot be the correct approach because it would go against the agreed terms between the parties at the time they concluded their contract. The interaction between these two provisions needs to be assessed on a case-by-case basis.

That in order for consent to additional or different terms to be manifested, the relevant conduct must be unequivocal. In C 29-3, the party’s conduct was not directly related to the alleged modification and thus no agreement could be established.

The behaviour and statements of the parties concerned. If behaviour and statements of the parties do not support a conclusion that the contract has been terminated, this is a relevant factor.

(a) Yes, there was a valid modification.

(b) The modification came about by a representative of the buyer counter-signing the seller’s general conditions of sale.

In Chateau des Charmes Wine, there was no conduct indicating assent to the change.

A merger clause excludes any external information and provides that the written contract contains the entirety of the agreement between the parties. A written modification clause states that any modifications to the contract must be made in writing. They are similar to the extent that they both provide for the exclusivity of the written contract. However, the clauses have different purposes: a merger clause excludes extrinsic evidence, whereas a written modification clause allows subsequent modifications to be made in writing.

(a) Whether the Respondent could have relied on an oral promise that the goods would be delivered before the expiry of the US import licenses.

(b) Article 29(2) was relied on by the arbitral tribunal in holding that the Respondent could not rely on an oral promise that the goods would be delivered at a date different to the date set out in the contract. 

(a) Parties may become bound by a particular course of dealing over a long-term relationship that may override a written modification clause within the meaning of Article 29(2) CISG.

(b) No, the explicit terms of the written contract prevail over any usage of trade.

(a) The buyer’s order form had been amended by the Austrian standard B 2110 form concerning the writing requirement for changes to the contract. As the parties’ actions complied with the standard form requirements, the contract had been validly modified.

(b) The seller’s objections were too late because they were not sent until six weeks later.

(a) The decision in C 29-8 is reminiscent of the common law equitable principle of estoppel, although the court did not hold that the party had to show detriment.

(b) That “conduct” can also extend to statements made in correspondence, as in that case.

(c) Presumably the outcome would have been different if the buyer had not obtained the guarantee, because in that case the provisions of the contract would have prevailed and there would have been no need to invoke the second sentence of Art 29(2) CISG.