In this particular case, a company incorporated under the Belgian Law ordered 761m² of granite cobblestones to a French company. The latter delivered and invoiced 800m². The Belgian buyer refused to pay the balance of sale of the goods invoking Article 19.1 of the 1980 Vienna Convention according to which an addition or a modification must be considered not as an acceptance of the offer but as a counter-offer which has to be accepted by the offeror for the contract to be validly concluded.

However, according to Article 19.2 and 19.3 of the same convention, a reply to an offer which purports to be an acceptance but which contains additional terms (price, payment, quality and quantity of goods, place and time of delivery) or different terms which do not materially alter the terms of the offer shall constitute an acceptance unless the offeror, without undue delay, objects to the discrepancy verbally or in writing. If he does not so object, the terms of the contract shall be the terms of the offer with the modifications contained in the reply of the recipient of the offer.

In its ruling, the Supreme Court considers the sale as being validly concluded: the seller’s reply to the buyer did not materially alter the terms of the order, the buyer having not objected to the discrepancy between his offer and the seller’s counter-offer.

A reply to an offer, which contains an addition or modification which does not materially alter the offer, shall therefore constitute an acceptance so that the contract is concluded.