b. Exception in Case of Immaterial Alterations
This general rule does, however, not always lead to adequate results. Particularly, where the alterations are of little or no importance to the other party there is no reason to prevent the contract from being concluded. Accordingly, Art. 19(2) makes an exception from the general rule for immaterial alterations:
(2) However, a reply to an offer which purports to be an acceptance but contains additional or different terms which do not materially alter the terms of the offer constitutes an acceptance, unless the offeror, without undue delay, objects orally to the discrepancy or dispatches a notice to that effect. If he does not so object, the terms of the contract are the terms of the offer with the modifications contained in the acceptance.
If the alteration is immaterial a contract is concluded with the alteration contained in the acceptance unless the offeror objects orally or in writing. In the latter case it is sufficient that the respective notice is dispatched; it does not have to reach the offeree, Art. 27. The objection has to be made without undue delay. While this phrase gives a certain degree of flexibility to take into account the individual circumstances, in general the objection has to be made within three days.
Which alteration of contractual terms is material and which is not is difficult to determine. In the first place, obviously the expectations of the parties are to be taken into account. In that regard, an alteration made by the offeree favoring the offeror is likely to be considered immaterial. Depending on the circumstances of the particular case, examples include changes in delivery or payment dates of a few days, or minor alterations to the shipping details or packaging requirements.
Art. 19(3) sheds some more light on the classification of alterations as material or immaterial:
(3) Additional or different terms relating, among other things, to the price, payment, quality and quantity of the goods, place and time of delivery, extent of one party's liability to the other or the settlement of disputes are considered to alter the terms of the offer materially.
In this regard it is important to note that Art. 19(3) only creates a rebuttable presumption that the alterations affecting the elements listed there are considered material. If the parties perform a contract despite the fact that the acceptance altered a term relating to an aspect listed in Art. 19(3) this subsequent behavior – of course depending on the individual circumstances of the case – can under Art. 8(3) lead to the interpretation that the parties considered the alteration nevertheless to be an immaterial one with the consequence that the contract was validly concluded via Art. 19(2) since no objection was made.