This study turns the facts of the condictio ob rem upside down. The concept of "legal transaction", codified in Section 812 (1) sentence 2 alt. 2 of the German Civil Code (BGB), has long been marginalised as a mere appendage to the laws governing contractual obligations and even called anti-systemic. Contrarily, historical-genetic analyses and dogmatic reconstructions show that the legal basis of the condictio ob rem constitutes a non-binding, causal contract with conditional links of its own. Through critiquing a legal doctrine dominated by debt and market exchange, Christoph Sorge points out an autonomous meaning of the condictio ob rem within traffic and property law.