[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).]
219. Under the main Convention rule which governs the buyer's right to avoid, the buyer is entitled to avoid only by reason of the seller's fundamental breach. This rule covers cases of non-delivery, late delivery and non-conformity as well.
However, in cases of non-delivery (only), the buyer may also avoid for another reason, i.e., if the seller does not deliver the goods within an 'additional period of time' fixed by the buyer, and CISG Article 47(1) describes the kind of additional period which may be fixed: 'The buyer may fix an additional period of time of reasonable length for performance by the seller of his obligations.'
Those who drafted the main CISG avoidance rule, which gives the buyer the right to terminate only in the event of a 'fundamental' breach, envisioned situations where the buyer might have reason to doubt whether the seller would perform before a given delay in delivery becomes truly serious (i.e., a 'substantial detriment' which would entitle the buyer to avoid); indeed, the buyer might have reason to doubt how the Convention requirement of fundamental breach would be applied to the circumstances of a given case.
For these reasons - and having been inspired by the similar (but not fully corresponding) Nachfrist provisions in German law - the CISG drafters gave the buyer the right to fix an additional period of time, after which the buyer may avoid without having to determine whether the total delay actually has reached 'fundamental' proportions. On the other hand, the flexible requirement that the period so fixed be 'reasonable' may tend to introduce a new element of uncertainty, especially since a variety of factors must enter into the calculation of whether the period fixed is to be judged 'reasonable' or not.
The Nachfrist notice is designed to give the seller in breach a second delivery chance; once sent, the buyer must await the seller's reaction. During the period fixed, buyer may not resort to any remedy he might otherwise have by virtue of the breach. [page 120]
As already emphasized, the seller's non-compliance with a given Nachfrist notice is sanctioned only in the case of non-delivery; only in this kind of Nachfrist situation will the buyer be entitled to avoid. Thus, although the broad wording of Article 47(1) would seem to comprise any breach, the practical application of the provision is limited to cases involving non-delivery.