Chantal Niggemann 
a. Parties to international contracts need to be able to rely on their agreement. Therefore, they need to know whether there are any formal requirements which have to be met for their agreement or its amendment to be valid. Some jurisdictions ask for specific form or comparable requirements to be met for the validity of commercial sales contracts, whereas most legal systems opt for the rule of consensualism, i.e., freedom of form.
During the deliberations of UNCITRAL for the elaboration of the CISG, one of the most controversial issues at the Vienna Conference was whether or not the principle of freedom of form of article 15 ULIS should be incorporated in the text of the CISG. Finally, a compromise was adopted with freedom of form as a basic rule and the reservation clause of articles 12 and 96 CISG. Where at least one of the parties to the contract has its place of business in a reservation State and a court of that State hears the case, the court must determine the law applicable to form according to its conflict of law rules, just as a court of another State, which did not adopt the CISG.
Although the issue of freedom of form might as well have been regulated in Part II of the CISG dealing with the formation of the contract, it has been integrated as a general provision and, therefore, also applies in case a party has its place of business in a State that declared a reservation under article 92 CISG.
The UNIDROIT Principles opted for unconditional freedom of form, which is expressed in articles 1.2 and 3.2 of the UNIDROIT Principles.
b. Article 1.2 of the UNIDROIT Principles merely refers to the writing requirement of contracts, whereas Article 11 sentence one CISG states that the contract is not subject to "any other requirement as to form", i.e., not only writing requirements. However, this difference is only in appearance, since although article 1.2 of the UNIDROIT Principles mentions only the requirement of writing, it has to be extended to other requirements as to form. Moreover, article 1.2 of the UNIDROIT Principles is to be seen in conjunction with article 3.2 of the UNIDROIT Principles, stating that a contract is concluded "without any further requirement".
Article 3.2 of the UNIDROIT Principles seems to go even beyond the scope of article 11 CISG, since in comparison to article 11 CISG, which names requirements "as to form", article 3.2 of the UNIDROIT Principles does not contain such a restriction. It is, however, undisputed that article 11 CISG also includes quasi-formal requirements such as consideration as is to be found in common law systems. The commentary to article 3.2 of the UNIDROIT Principles makes it clear that are also excluded is the requirement of cause which exists in some civil law systems, as well as rules regarding so-called real contracts, which require the handing over of goods for their conclusion. Although the exclusion of the cause requirement and the real-contract rules is not discussed under the Convention, the same should apply and they should be displaced by the principle of freedom of form of article 11 CISG.
c. Both the UNIDROIT Principles in article 1.2, second sentence, and the CISG in article 11, second sentence, make clear that the principle of freedom of form implies the admissibility of oral evidence in judicial proceedings. The language of both clauses is perfectly identical, as is their understanding in the commentaries. Article 1.2 second sentence of the UNIDROIT Principles may, therefore, merely support the interpretation of article 11 sentence two CISG.
d. According to article 6 CISG, the parties are of course also free to agree, orally or in writing, on specific form requirements to be met for the validity of the contract and which might also to be applied for modifications and/or termination. This is also expressed in article 2.13 of the UNIDROIT Principles, and the illustrations contained in the Official Comments to article 2.13 of the UNIDROIT Principles may be helpful in the interpretation of article 11 in this respect. In this regard and concerning written modification clauses, please refer to the Editorial remarks regarding article 29 CISG.
e. In case one of the parties confirms the content of a contract, whereby such confirmation contains additional or different terms, the question arises whether such terms may become part of the contract in case the confirmation is not in writing, i.e., whether article 11 CISG and the concept of freedom of form also applies to such confirmation. The CISG does not explicitly deal with this issue. In case the rules for Commercial letters of confirmation (kaufmännisches Bestätigungsschreiben) apply, e.g., as usages by which the parties are bound (see article 9 CISG), scholars and tribunals tend to ask for a written confirmation, whereby article 2.12 of the UNIDROIT Principles deals with such a confirmation and explicitly requires it to be in writing.
f. Article 11 CISG only applies to the formation of the contract, not to its modification or termination as does article 3.2 of the UNIDROIT Principles. With regard to the manner in which the UNIDROIT Principles may be used to interpret or supplement aarticle 29 CISG for modifications and termination, please see the Editorial remarks regarding article 29 CISG.
g. As a result it can be said that the intent of article 11 CISG is reproduced in article 1.2 read in conjunction with 3.2 of the UNIDROIT Principles. Thereby, the Official Comments of articles 1.2 and 3.2 of the UNIDROIT Principles support the interpretation of article 11 CISG. In addition, articles 2.12 and 2.13 of the UNIDROIT Principles assist the further interpretation of freedom of form under article 11 CISG.
1. Legal Counsel at Techem Energy Services GmbH & Co. KG, an international service provider in the field of measuring and billing of energy and water consumption with its place of business near Frankfurt am Main, Germany.
2. Schlechtriem, Uniform Sales Law - The UN-Convention on Contracts for the International Sale of Goods, 1986, p. 43 subs., available at <http://cisgw3.law.pace.edu/cisg/biblio/schlechtriem.html>.
3. Schlechtriem in v. Caemmerer/Schlechtriem, Kommentar zum Einheitlichen UN-Kaufrecht -CISG-, 3rd ed. 2000, Art. 12 at marginal note 2 with further citations; Melis in Honsell, Kommentar zum UN-Kaufrecht, 1997, Art. 12 at marginal note 4.
4. Magnus in Staudinger, Kommentar zum BGB - Wiener UN-Kaufrecht (CISG), 1999, Art. 11 at marginal note 6; Witz in Witz/Salger/Lorenz, International Einheitliches Kaufrecht, 2000, Artt. 11-12 at marginal note 2; Heuzé, La vente internationale de marchandises, 1992, at note 196; see also Honnold, Uniform Law for International Sales under the 1980 United Nations Convention, 3rd ed. 1999, Art. 11 at note 127.1.
5. This principle of freedom of form may, however, be overridden by mandatory rules of the applicable law, see article 1.4 of the UNIDROIT Principles and note 2 of the Official Comments of article 1.2.
6. Official Comments on articles of the UNIDROIT Principles, article 1.2 at note 1.
7. Witz, loc. cit., Artt. 11-12 at marginal note 5; Schlechtriem in v. Caemmerer/ Schlechtriem, loc. cit., Art. 11 at marginal note 11; Magnus, loc. cit., Art. 11 at marginal note 9; see also Secretariat Commentary Art. 27 note. 2 referring to article 29 CISG.
8. Official Comments on articles of the UNIDROIT Principles, article 3.2 at notes 2 and 3. With regard to the requirement of cause, other effects which may derive from it such as its illegality are not concerned.
9. Schlechtriem in v. Caemmerer/Schlechtriem, loc. cit., Art. 11 at marginal notes 12 and 13 with further reference; Official comments on articles of the UNIDROIT Principles, article 1.2 at note 1.
10. Honnold, loc. cit, Art. 11 at note 127; Schlechtriem in v. Caemmerer/Schlechtriem, loc. cit., Art. 11 at marginal note 16; Melis in Honsell, loc. cit., Art. 11 at marginal note 3; Rajski in Bianca/Bonell, Commentary on the International Sales Law, 1987, Art. 11 at note 3.1.
11. Official Comments on articles of the UNIDROIT Principles, article 2.13 at note 2.
12. Schlechtriem in v. Caemmerer/Schlechtriem, loc. cit., Art. 11 at marginal note 6; Civil Court Basel, judgment dated 21 December 1992, in application of Austrian and Swiss legal rules regarding writings in confirmation, in BJM 1993, p. 310 subs.