ABSTRACT
It will be recalled that in German law, problems of failure of contractual counterperformance generally belong to the law of Rücktritt. However, we have seen that if a contract has been avoided ab initio, the restitutionary consequences will be governed by the general law of unjust enrichment in §§ 812 ff. In these cases the contract is treated as though it had never existed. Performances made causa solvendi, for the purpose of discharging it, have not in the event achieved that purpose. The ‘legal ground’ of the enrichment has thus fallen away. Whether a contract is void ab initio or merely ineffective therefore determines whether the general enrichment claim in § 812 I or the more specialised enrichment claim in § 346 will lie under the name of Rücktritt.
