The book deals with problems of the conditional sale. An important area is dedicated to the problem of one party remaining silent to the other party's offer. In this context cases are examined where a reservation of proprietary rights can be assumed; special focus is put on the so-called "conflict of general business terms". The main focus is set on the question whether proprietary rights can be reserved by the vendor's mere declaration. The answer to this can be of enormous interest to the vendor: If possible, he can gain a valid security in case of the purchaser's bankrupcy. Therefore, the idea of a "contract in rem" and its meaning for the transfer of ownership is analysed. The final conclusion is that a reservation of proprietary rights is only possible if the vendor has the defence of the purchaser's insecurity.