The two most popular traditions in Western political philosophy are inadequate to justify the authority governments wield over individuals, German philosopher Jurgen Habermas asserted in the second and last of the annual Tanner lectures last night in Sanders Theater.

Habermas presented a detailed history and critique of both the theory of the social contract, which states that government is a contract among individuals who leave a state of nature, and the theory of natural law, which asserts that there are certain fundamental and inalienable rights.

Habermas said that both of these theories "try to derive all principles from rationality, but run aground on the complexity" of modern capitalist states. Modern societies change too rapidly for any social contract or set of fundamental laws to remain viable, he said.

There must be a recognition of the moral values that law presupposes, Habermas said.