ABSTRACT
Mistake plays a fundamental role in the German law of unjust enrichment. It is as true for German law as it is for English law that a mistaken payment or transfer can be recovered back. If the role of mistake in German enrichment law is sometimes underestimated, this is mainly for two reasons. First, § 119 BGB, which is the central provision relating to mistake in the code, appears to be concerned exclusively with contracts. Secondly, the law of unjust enrichment is structured in such a way that the true reason for restitution, be it mistake, duress, failure of consideration or some other reason, is hidden behind the abstraction ‘without legal ground’. Nevertheless, mistake is relevant in the context of unjust enrichment in the following ways:
First and most obviously, where a contract is avoided because of a mistake under § 119 BGB, any performances which have already been rendered in accordance with the contract will be recoverable under §§ 812 ff BGB: the contract is now void, the ‘legal ground’ of the enrichment has thus fallen away and restitution will follow. The true reason for restitution is nevertheless the mistake: without the mistake, the contract would have continued to subsist. § 812 BGB would have had nothing to say. It is thus not surprising that most cases turning on the application of § 119 are in reality unjust enrichment cases, the claimant seeking restitution of a benefit transferred pursuant to a contract. In order to decide whether restitution is available under § 812 I, the court will first have to decide whether or not to set aside the contract on the basis of § 119. Thus, a case decided in 1980,1 which shall serve as one example out of many, involved the sale of a harvester. The buyer argued that he had been mistaken about the age of the machine, and asked for his money back. The action was based on § 812 I, but before that provision could be applied, the court first had to consider the question whether a mistake as to the year of manufacture of goods bought was a relevant mistake under § 119 II. Having answered this question in the affirmative, the court worked out the restitutionary consequences of the buyer’s successful rescission of the contract of sale.
