[For more current case annotated texts by this author, see Bernstein & Lookofsky, Understanding the CISG in Europe, 2d ed. (2003) and Lookofsky, Understanding the CISG in the USA, 2d ed. (2004).]
I. Acceptance: Indication of Assent
112. Paragraph (1) of Article 18 tells us which kinds of statement constitute a true acceptance:
113. According to the rule in paragraph (1), an acceptance may consist of a statement or of other conduct, e.g., shipping goods which the buyer has offered to buy. Whatever the form, for a statement or conduct to constitute an acceptance, it must provide some indication of the offeree's assent.
On the other hand, since the CISG does not impose upon the offeree a general duty to reply, silence or inactivity does not - in itself - amount to acceptance. Therefore, the offeror cannot bind the offeree in advance merely by stating that silence will be treated as an indication of the offeree's assent. Then again, if the offeree initiates a transaction by soliciting an offer, he - the offeree - may bind himself in advance by indicating that an offer received will be deemed accepted absent contrary indication by the offeree within a specified period.
II. Time Acceptance Takes Effect
A. When Assent Reaches Offeror
114. Paragraph (2) of Article 18, which determines the point in time at which an acceptance (under the first paragraph) becomes effective, provides as follows:
By virtue of the rules set forth in paragraph (2), an acceptance becomes effective upon the timely anival of the offeree's indication of assent. In other words, to be effective, the acceptance must arrive, and it must arrive 'in time'.
B. Receipt Theory
115. An important consequence of the 'receipt theory' of acceptance, as adopted by the CISG in Article 18(2), is that the sender of the acceptance (the offeree) must bear the risk of transmission, i.e., the risk that the acceptance may never really arrive, e.g., if the acceptance is lost in the mail. In other words, absent contrary prior agreement, the offeree's notice of acceptance must in some manner actually reach the offeror, in order to bring about the legal consequences generally associated with the acceptance of a CISG offer.
C. Acceptance Within Time Fixed or Reasonable Time
116. In accordance with the principle that the offeror is the master of the offer, the acceptance must reach the offeror within the time which the offeror has fixed.[l] If no time has been fixed, the CISG default rule is that the acceptance must reach its destination within a 'reasonable' time, taking due account of all the circumstances. Thus, an offer sent by telefax will require a more prompt reply than an offer sent by post. Absent contrary indication, an oral offer requires an 'immediate' acceptance.
D. Assent By Performance of Act
117. As regards the time at which acceptance takes effect, paragraph (3) of Article 18 provides for cases where the offeree assents by performing an act:
In many cases, the offeror will call upon the offeree to 'indicate assent' by a statement of intention, i.e., a notification which serves as a promise by the offeree to act at some future point in time.
Sometimes, however, the offeror will request - or at least impliedly condone that the offeree accept without actually making such a statement. For example, the offeror may request or condone that the offeree accept by performing an act, e.g. shipping the goods ordered by the offeror. A similar understanding may follow from a 'course of dealing' established between the particular parties concerned or from a broader usage among merchants within the particular trade.
In all such cases, assuming the act is performed within the time fixed by the offeror or within a reasonable time, the offeree's acceptance becomes effective at the moment the act is actually performed. And from this it follows that the offeror cannot revoke (even an otherwise revocable offer) if the purported revocation reaches the offeree after the act requested has been performed.