The Convention governs only the formation of the contract of sale and the rights and obligations of the seller and buyer arising from such a contract. In particular, except as otherwise expressly provided in this Convention, it is not concerned with

  • a The validity of the contract or any of its provisions ... 963

So, whereas issues relating (e.g.) to the revocability of offers are clearly governed by CISG Part II, and issues relating (e.g.) to delayed or nonconforming delivery are clearly governed by CISG Part III, issues relating to unconscionable or unreasonable contract terms (which are not CISG-governed) can only be resolved by domestic law. Indeed:

‘The drafters’ purpose in creating the ‘validity’ exception ... was to preserve the applicability of national rules deemed important enough by individual states that the rules were not, under the state’s domestic law, subject to contrary agreement of the parties.’ 964

The scope of the validity exception is, nonetheless, a matter of considerable dispute. Indeed, when it comes to a CISG liability ‘exemption’ due to an ‘impediment’ to performance, some scholars – emphasizing the ‘except clause’ in CISG Article 4(a) 965 and/or the ‘uniformity principle’ in Article 7(1) – argue that Article 79 precludes the application of ‘competing’ domestic validity rules. More about this in the following.

4. Impracticability

Assuming, for the sake of argument, that the parties have concluded a ‘reasonable’ agreement, those parties are bound to perform. After all, ‘a deal’s a deal.’ 966

By way of exception, however, one of the promisors concerned may later claim (s)he is entitled to an excuse for nonperformance – this by virtue