국제계약법 원칙상의 변경된 승낙

In commercial dealings it often happens that the offeree, while signifying to the offeror its intention to accept the offer (“acknowledgement of order”), nevertheless includes in its declaration terms additional to or different from those of the offer. Most principles of international contract law provides that such a purported acceptance is as a rule to be considered a rejection of the offer and that it amounts to a counter-offer by the offeree, which the offeror may or may not accept either expressly or impliedly, e.g. by an act of performance. The principle according to which the acceptance must be the mirror image of the offer implies that even unimportant differences between the offer and the acceptance permit either party at a later stage to question the existence of the contract. In order to avoid such a result, which a party may well seek merely because market conditions have changed unfavourably, CISG, PICC or PECL provides for an exception to the general rule laid down in mirror image rule by stating that if the additional or modified terms contained in the acceptance do not “materially” alter the terms of the offer, the contract is concluded with those modifications unless the offeror objects without undue delay. What amounts to a “material” modification cannot be determined in the abstract but will depend on the circumstances of each case. Additional or different terms relating to the price or mode of payment, place and time of performance of a non-monetary obligation, the extent of one party’s liability to the other or the settlement of disputes, will normally, but need not necessarily, constitute a material modification of the offer. An important factor to be taken into account in this respect is whether the additional or different terms are commonly used in the trade sector concerned and therefore do not come as a surprise to the offeror.