If marriage itself is regarded as an arbitrary contract and as grounded not in natural law but merely in the natural sexual drive, and if external reasons for monogamy have been derived even from the physical relation between numbers of men and women, and obscure feelings have been cited as the only reason for prohibiting marriage between blood relations, such arguments are based on the common notion Vorstellung of a state of nature and of the naturalness of right, and on the absence of the concept of rationality and freedom.