(1) The parties are bound by any usage to which they have agreed and by any practices which they have established between themselves. 


(2) The parties are bound by a usage that is widely known to and regularly observed in international trade by parties in the particular trade concerned except where the application of such a usage would be unreasonable.




1. Practices and usages in the context of the Principles


This Article lays down the principle according to which the parties are in general bound by practices and usages which meet the requirements set forth in the Article. Furthermore, these same requirements must be met by practices and usages for them to be applicable in the cases and for the purposes expressly indicated in the Principles (see, for instance, Articles 2.1.6(3), 4.3, and 5.1.2).


2. Practices established between the parties


A practice established between the parties to a particular contract is automatically binding, except where the parties have expressly excluded its application. Whether a particular practice can be deemed to be “established” between the parties will naturally depend on the circumstances of the case, but behaviour on the occasion of only one previous transaction between the parties will not normally suffice.




1. A, a supplier, has repeatedly accepted claims from B, a customer, for quantitative or qualitative defects in the goods as much as two weeks after their delivery. When B gives another notice of defects after a fortnight, A cannot object that it is too late since the two-weeks’ notice amounts to a practice established between A and B which will as such be binding on A.


3. Agreed usages


By stating that the parties are bound by usages to which they have agreed, paragraph (1) of this Article merely applies the general principle of freedom of contract laid down in Article 1.1. Indeed, the parties may either negotiate all the terms of their contract, or for certain questions simply refer to other sources including usages. The parties may stipulate the application of any usage, including a usage developed within a trade sector to which neither party belongs, or a usage relating to a different type of contract. It is even conceivable that the parties will agree on the application of what sometimes misleadingly are called usages, i.e. a set of rules issued by a particular trade association under the title of “Usages”, but which only in part reflects established general lines of conduct.


4. Other applicable usages


Paragraph (2) lays down the criteria for the identification of usages applicable in the absence of a specific agreement by the parties. The fact that the usage must be “widely known to and regularly observed [...] by parties in the particular trade concerned” is a condition for the application of any usage, be it at international or merely at national or local level. The additional qualification “in international trade” is intended to avoid usages developed for, and confined to, domestic transactions also being invoked in transactions with foreigners.




2. A, a real estate agent, invokes a particular usage of the profession in its country vis-à-vis B, a foreign customer. B is not bound by such a usage if that usage is of a local nature and relates to a trade which is predominantly domestic in character.

Only exceptionally may usages of a purely local or national origin be applied without any reference thereto by the parties. Thus, usages existing on certain commodity exchanges or at trade exhibitions or ports should be applicable provided that they are regularly followed with respect to foreigners as well. Another exception concerns the case of a businessperson who has already entered into a number of similar contracts in a foreign country and who should therefore be bound by the usages established within that country for such contracts.




3. A, a terminal operator, invokes a particular usage of the port where it is located vis-à-vis B, a foreign carrier. B is bound by this local usage if the port is normally used by foreigners and the usage in question has been regularly observed with respect to all customers, irrespective of their place of business and of their nationality.


4. A, a sales agent from Country X, receives a request from B, one of its customers in Country Y, for the customary 10% discount upon payment of the price in cash. A may not object to the application of such a usage on account of its being restricted to Country Y if A has been doing business in that country for a certain period of time.


5. Application of usage unreasonable


A usage may be regularly observed by the generality of business people in a particular trade sector but its application in a given case may nevertheless be unreasonable. Reasons for this may be found in the particular conditions in which one or both parties operate and/or the atypical nature of the transaction. In such cases the usage will not be applied.




5. A usage exists in a commodity trade sector according to which the purchaser may not rely on defects in the goods if they are not duly certified by an internationally recognised inspection agency. When A, a buyer, takes over the goods at the port of destination, the only internationally recognised inspection agency operating in that port is on strike and to call another from the nearest port would be excessively costly. The application of the usage in this case would be unreasonable and A may rely on the defects it has discovered even though they have not been certified by an internationally recognised inspection agency.


6. Usages prevail over the Principles


Both courses of dealing and usages, once they are applicable in a given case, prevail over conflicting provisions contained in the Principles. The reason for this is that they bind the parties as implied terms of the contract as a whole or of single statements or other conduct on the part of one of the parties. As such, they are superseded by any express term stipulated by the parties but, in the same way as the latter, they prevail over the Principles, the only exception being those provisions which are specifically declared to be of a mandatory character (see Comment 3 on Article 1.5).

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