It is often overlooked that a contractual relationship is not solely governed by the text that the parties have (possibly) agreed upon and that the transaction must be interpreted on the basis of the conduct of the contracting parties before and after conclusion, as well as that the same may be supplemented by any customs and habits practised in the commercial sphere where the contracting parties operate.

The subject of the integration of the contract is, of course, regulated by both the Vienna Convention (CISG) and the Civil Code, with differences that are certainly not negligible; the choice of whether or not to apply the Convention to a given relationship has rather significant practical repercussions that are briefly analysed below.

- Read also: When the Vienna Convention applies.

1. Vienna Convention

Article 9 of the Vienna Convention states that:

"The parties are bound by the usages [practices] to which they have agreed and by the customs [usages] established between them.

Unless the parties have agreed otherwise, they shall be deemed to have tacitly referred in the contract and in its drafting to any usage of which they were or ought to have been aware and which, in international trade, is widely known and regularly observed by the parties in contracts of the same kind, in the trade concerned. "

According to this provision, the parties to an international sales contract are bound by both customs ("practices"), as well as to practices ("usages"), which the contracting parties have (expressly or implicitly)[1] established between them. Although the convention does not define the concepts of usages e practicesthey can be translated as follows:

  • "practices"with individual customs, i.e. commercial practice[2] established between the contracting parties in their previous contractual relations;[3]
  • "usages", with negotiated usages, or customs, understood as conduct normally practised in a certain commercial sphere, with the belief that it is binding conduct.

According to Art. 9 para. 1 of the CISCG, both the "practices", that the "usages" do not have a mere interpretative value, but must even be considered an integral part of the contractual relationship, albeit subject to certain limitations and conditions, which will be analysed below. Before doing so, for the sake of clarity, some "practices" that were deemed applicable between the parties:

  • the obligation of a seller to promptly deliver spare parts to the buyer, based on the practice that had been established between them;[4]
  • it was held that a seller could not invoke the rule in Article 18 CISG that silence does not amount to acceptance, given that the parties had established an internal practice whereby the seller executed the buyer's orders without the need for express acceptance;[5]
  • in another case, also for the purpose of reporting defects, it was decided that the purchaser was bound to a certain manner of examining the delivered goods on the basis of a practice that had been established over time.

But when are such practices?

First of all, it is necessary to understand whether a real ''relationship'' has actually been established between the parties.practice" and, in order to do so, it is necessary that the particles have been conducted with such frequency and over such a period of time as to cause the party invoking them to believe and presume in good faith that they would be perpetuated over time.[6]

Once this 'preliminary' element has been ascertained, it is indeed necessary to verify whether there are any contractual provisions between the parties that exclude their applicability, or whether there are contractual agreements that are in fact contrary to the practice allegedly established between the contracting parties.

In fact, although according to a jurisprudential orientation[7] usages and customs would even derogate from the provisions of the Convention, if the parties have excluded their application, or have inserted clauses that in fact conflict with them, negotiated agreements would prevail over usages. This principle follows from Article 6 of the CISG, according to which the will expressed by the contracting parties is the primary source of the rights and obligations arising from contracts concluded under the CISG.[8]

Thereafter, the onus will be on the party claiming its existence to prove the required elements,[9] with the consequence that in the event of failure to do so, custom and practice will not be binding between the parties.

Once its existence has been proven under the Convention, its legitimacy must be assessed according to the domestic law applicable in each case, so that the validity of usages does not fall within the scope of the Convention, which only regulates the criteria for their applicability.[10]

As for commercial uses (usages), which, on the other hand, are those customs that are normally practised in a certain mercantile environment, the parties are bound to them, pursuant to Art. 9(2), even in the absence of an express agreement transposing them, provided that they "were or should have been aware'..

As a general rule, international trade usages should only be considered binding if they are widely known to the parties, or if they are regularly observed in international trade.[11] It should also be noted that for a usage to be binding it does not have to be international, but local usages used e.g. in stock exchanges, trade fairs, warehouses, may also be applicable to the relationship, provided that they are also regularly applied in transactions involving foreign contracting parties.[12]

One decision was even held that the usages are automatically included in any agreement governed by the Convention unless expressly excluded by the parties.[13]

Also for the usages, the principle applies that they (if applicable) derogate from the provisions of the Convention that differ therefrom, but not from conflicting contractual agreements, contractual autonomy being the primary source of the rights and obligations of the parties.

As to the burden of proof, it is held that there is no difference in the allocation of the burden of proof under Art. 9(1) and (2), since the party claiming the existence of usages or practices binding, it must nevertheless prove the elements required by it.[14]

2. Civil Code

Certainly less linear and decidedly more complex is the civil law regulation of usages and customs, which are categorised into:[15]

  • Regulatory usesgoverned by arts. 1 and 8 of the lexis. These are all the unwritten rules that a given social environment consistently observes over time as legally binding rules.[16] Such usages apply to matters not regulated by laws or regulations, or to the extent to which they are referred to therein.
  • Contractual Uses, negotiations or usage clauses, as referred to in Art. 1340 of the Civil Code. To be understood as practices as commonly and consistently observed in contractual transactions in a given place or branch of trade. Such usages may be equated with "usages' referred to in the Vienna Convention.
  • Individual uses, are the practice established in relations between certain parties and relevant to the interpretation of the contract, pursuant to Art. 1362(2) of the Civil Code (assimilated to the "practices"of the CISC).

While understanding in detail the distinction between regulatory uses and contracts would certainly require a more careful and thorough examination, but for the purposes of the present article, it may be simplified by stating that the statutory usages are those applicable whenever the law refers to them (e.g. in the matter of sale, Art. 1498, para. 2 of the Civil Code on the manner of payment of the price), or when there are matters not regulated by the law itself, in which case they play an integrative function (usages praeter legem).

The negotiated uses on the other hand, are generalised business practices that are intended to be included in the contract if it does not appear that they were not intended by the parties (Art. 1340 Civil Code).[17]  Such usages may, for instance, provide for the variability of the quantity or quality of the goods within certain tolerance limits, or the obligation to return the containers of the goods bought and sold, or the possible acknowledgement of a performance guarantee; in the international sphere, the uniform rules and usages of the International Chamber of Commerce in the field of documentary credits have been regarded as negotiating usages.[18]

Moreover, unlike statutory usages, negotiated (or contractual) usages apply without the need for a statutory reference: the law contains, in fact, in Art. 1374 of the Civil Code (integration of the contract) a general reference to usages as a source of integration of the contract, since the parties are bound by what is determined by the agreement and by all the consequences arising therefrom according to the law or, failing that, according to usages.

A first and important difference is related to the fact that negotiated uses (as opposed to usages which are applicable whenever the same were known or knowable to the parties at the time of the conclusion of the contract) in civil law the jurisprudence is not in agreement as to whether they can be deemed to be incorporated into the contract only by virtue of an express or tacit manifestation of the parties,[19] or whether the uses oblige the parties even if ignored by them.[20]  It may, however, be reasonably argued that such usages are also effective in derogation of (obviously non-mandatory) statutory provisions, but that they must be excluded in the event of a contrary, agreed will of the parties, even if tacitly expressed.[21]

Negotiated uses must also be distinguished from individual usesi.e. the practice established in relations between certain contracting parties (the practices of the CISG).

Very important to note that, contrary to the practices, the internal practice of the contracting parties is only relevant for the interpretation of the contract, as the overall conduct of the parties (Art. 1362 para. 2 CC),[22] but does not also incorporate its contents under Article 1340 and Article 1374 of the Civil Code.[23]

It follows, therefore, that unlike Art. 9 of the CISC, the bargaining practice established between the parties cannot have the value of an actual contractual clause forming an integral part of the relationship, but can only be used as an element to interpret the contract. Difference, far from negligible.

One way of nevertheless attempting to pursue the same result, i.e. to integrate a given individual practice within the relationship, would be to have recourse to the principle of equity, referred to in Article 1374 of the Civil Code, which provides as follows:

"The contract binds the parties not only to what is expressed therein, but also to all consequences arising therefrom according to law, or, in the absence thereof, according to usage and equity the parties shall be bound by it. uses and theequity. "

Using this principle, coupled with the principle of performance in good faith of the contract under Art. 1375 of the Civil Code, one could possibly attempt to argue that the continued and repeated conduct of one party has engendered in the other the expectation that the same would be repeated.

Certainly, such a solution would still be much more complex and difficult to implement than if the Vienna Convention were to apply to the relationship, given that the provisions of Article 9 are certainly much clearer and easier to interpret in this respect.

[1] Oberster Gerichsthoff 21 March 2000.

[2] See DE FRANCHIS, Dizionario Giuridico Itailano-Inglese, Giuffrè Editore,

[3] BUSANI, The International Sale and Purchase Agreement, p. 97 et seq., 2015, Giappichelli

[4] Court of Arbitration of the International Chamber of Commerce, France, December 1997 No. 8817,

[5] Cour d'appel de Paris, France, 10 September 2003

[6] UNCITRAL: Digest of Case Law on the United Nations Convention on Contracts for the International Sale of Goods-2016 UNITED NATIONS 2016 Edition.

[7] CLOUT case no. 313, Cour d'appel de Grenoble, France, 21.10.1999.

[8] See Hof van Beroep Antwerpen (Belgium), 24 April 2006; BUSANI, op. cit.

[9] Oberster Gerichtshof, Austria, 21 March 2000.

[10] Oberster Gerichtshof, Austria, 22 October 2001.

[11] UNCITRAL: Digest of Case Law on the United Nations Convention on Contracts for the International Sale of Goods-2016 UNITED NATIONS 2016 Edition.

[12] Oberlandesgericht Graz, Austria, 9 November 1995.

[13] U.S. District Court, Southern District Court of New York, 10 May 2002.

[14] UNICITRA Digest. Op. cit.

[15] For the sake of simplicity, no further categories, such as interpretative uses and business uses, are included in this article.

[16] BIANCA, Civil Law, The Contract, 1987, Giuffrè.

[17] BIANCA, op. cit.

[18] Cass. Civ. 2009, no. 21833

[19] Cass. Civ. 2010 no. 8342.

[20] Cass. Civ. 2007 no. 5135.

[21] Cass. Civ. 2007 no. 5135; Cass. Civ. 1988 no. 76.

[22] CIAN - TRABUCCHI, Commentary on the Civil Code, Art. 1340, CEDAM.

[23] Cass. Civ. 1988 no. 3220.