An unconscious discrepancy between intent and declaration can also occur when one of the contracting parties is in error. Error arises when the intended will diverges from the declared will, and neither party is aware of this divergence, or when there is merely an apparent difference between the intended and the declared will.112
An error is a false belief about a fact or a right (legal error). Legal error is generally not considered, while factual error may be taken into account only if it is essential and not caused by negligence (excusable error). An error is essential if it concerns the essential characteristics of the subject matter, the identity of the contracting party, or circumstances considered decisive according to trade customs or the intent of the parties, as the party in error would not have concluded the contract under those conditions otherwise.113
An error must be excusable and not due to negligence. A deviation from the required standard of care constitutes negligence. Even slight negligence is sufficient to prevent a party from relying on its error. In gratuitous contracts, an error in the motive that was decisive for assuming the obligation is also considered essential.
If a party entered into a contract due to a mistaken belief about an essential fact or believed that a decisive fact would materialise, they have the right to request annulment of the contract. However, annulment is not allowed if the party would have made the same decision with correct information.114 The party must prove its mistaken belief. If the mistake was caused by the other party’s actions or if the other party knew or should have known about the error, the mistake is deemed intentional.115
Example: A wants to buy a wine barrel from B because he expects to produce around 14 litres of wine. B tells A that the barrel has a capacity of 15 litres, even though it actually holds only 13.5 litres.
A mistake should be distinguished from a misunderstanding, which is regulated by Article 16 of the OZ. This provision applies to the following actual situation: 1. A misunderstanding exists between the parties. 2 The misunderstanding concerns a) the nature of the contract, b) the basis of the contract, or c) the subject of the obligation
Despite this, both parties believe they have reached an agreement. If these conditions are met, Article 16 of the OZ provides that the contract does not come into existence. This means that not all disagreements fall under the concept of misunderstanding. For example, disputes regarding the characteristics of the subject matter or the identity of the contracting party are not covered by Article 16 but are instead addressed in Article 46 of the OZ, which regulates error.116
