Official Comments
 Article #  

(Mode of acceptance)

(1) A statement made by or other conduct of the offeree indicating assent to an offer is an acceptance. Silence or inactivity does not in itself amount to acceptance.
(2) An acceptance of an offer becomes effective when the indication of assent reaches the offeror.
(3) However, if, by virtue of the offer or as a result of practices which the parties have established between themselves or of usage, the offeree may indicate assent by performing an act without notice to the offeror, the acceptance is effective when the act is performed.

Official Comment
 1. Indication of assent to an offer

For there to be an acceptance the offeree must in one way or another indicate “assent” to the offer. The mere acknowledgement of receipt of the offer, or an expression of interest in it, is not sufficient. Furthermore, the assent must be unconditional, i.e. it cannot be made dependent on some further step to be taken by either the offeror (e.g. “Our acceptance is subject to your final approval”) or the offeree (e.g. “We hereby accept the terms of the contract as set forth in your Memorandum and undertake to submit the contract to our Board for approval within the next two weeks”). Finally, the purported acceptance must contain no variation of the terms of the offer or at least none which materially alters them (see Article 2.1.11).

2. Acceptance by conduct

Provided that the offer does not impose any particular mode of acceptance, the indication of assent may either be made by an express statement or be inferred from the conduct of the offeree. Paragraph (1) of this Article does not specify the form such conduct should assume: most often it will consist in acts of performance, such as the payment of an advance on the price, the shipment of goods or the beginning of work at the site, etc.

3. Silence or inactivity

By stating that “[s]ilence or inactivity does not in itself amount to acceptance”, paragraph (1) makes it clear that as a rule mere silence or inactivity on the part of the offeree does not allow the inference that the offeree assents to the offer. The situation is different if the parties themselves agree that silence shall amount to acceptance, or if there exists a course of dealing or usage to that effect. In no event, however, is it sufficient for the offeror to state unilaterally in its offer that the offer will be deemed to have been accepted in the absence of any reply from the offeree. Since it is the offeror who takes the initiative by proposing the conclusion of the contract, the offeree is free not only to accept or not to accept the offer, but also simply to ignore it.


1. A requests B to set out the conditions for the renewal of a contract for the supply of wine, due to expire on 31 December. In its offer B includes a provision stating that “if we have not heard from you at the latest by the end of November, we will assume that you have agreed to renew the contract on the conditions indicated above”. A finds the proposed conditions totally unacceptable and does not even reply. The former contract expires on the fixed date without a new contract having been agreed between the parties.

2. Under a long-term contract for the supply of wine B regularly met A’s orders without expressly confirming its acceptance. On 15 November A orders a large stock for New Year. B does not reply, nor does it deliver at the requested time. B is in breach since, in accordance with the practice established between the parties, B’s silence in regard to A’s order amounts to an acceptance.

4. When acceptance becomes effective

According to paragraph (2), an acceptance becomes effective at the moment the indication of assent reaches the offeror (see Article 1.10(2)). For the definition of “reaches” see Article 1.10(3). The reason for the adoption of the “receipt” principle in preference to the “dispatch” principle is that the risk of transmission is better placed on the offeree than on the offeror, since it is the former who chooses the means of communication, who knows whether the chosen means of communication is subject to special risks or delay, and who is consequently best able to take measures to ensure that the acceptance reaches its destination.
As a rule, an acceptance by means of mere conduct likewise becomes effective only when notice thereof reaches the offeror. It should be noted, however, that special notice to this effect by the offeree will be necessary only in cases where the conduct will not of itself give notice of acceptance to the offeror within a reasonable period of time. In all other cases, e.g. where the conduct consists in the payment of the price, or the shipment of the goods by air or by some other rapid mode of transportation, the same effect may well be achieved simply by the bank or the carrier informing the offeror of the funds transfer or of the consignment of the goods.
An exception to the general rule of paragraph (2) is to be found in the cases envisaged in paragraph (3), i.e. where “by virtue of the offer or as a result of practices which the parties have established between themselves or of usage, the offeree may indicate assent by performing an act without notice to the offeror”. In such cases the acceptance is effective at the moment the act is performed, irrespective of whether or not the offeror is promptly informed thereof.


3. A asks B to write a special program for the setting up of a data bank. Without giving A notice of acceptance, B begins to write the program and, after its completion, insists on payment in accordance with the terms set out in A’s offer. B is not entitled to payment since B’s purported acceptance of A’s offer never became effective as B never notified A of it.

4. The facts are the same as in Illustration 3, except that in the offer B is informed of A’s absence for the following two weeks, and that if B intends to accept the offer B should begin writing the program immediately so as to save time. The contract is concluded once B begins to perform, even if B fails to inform A thereof either immediately or at a later stage.

This Article corresponds to paragraphs (1), (2) first part and (3) of Article 18 CISG.