THOUGH it seems like ancient history after the dramatic climax of Clarence Thomas's confirmation hearings, earlier in the proceedings a focus of controversy was Judge Thomas's views on "natural law." To many Americans the debate must have seemed arcane, something only law professors could love.Yet beneath the natural-law debate lies an issue central to the Bill of Rights. That is, do the "privileges or immunities" enjoyed by Americans and protected by the Constitution include rights not specifically enumerated in the charter? And if so, how are such unstated rights to be defined? Liberal opponents of Thomas expressed concern about his musings over the years on natural law. Some fear especially that Thomas may extract from his understanding of natural law a right to life that is violated by abortion. Yet liberals' concerns are ironic, given the great extent to which natural law - if not in so many words - has been invoked by liberal justices in fashioning much of modern jurisprudence on protected rights. In its landmark ruling outlawing segregated schools, the Warren Court accepted Thurgood Marshall's natural-law argument that separate schools are inherently unequal. More ironically still in the context of the Thomas debate, the right to privacy set forth in Supreme Court decisions protecting birth c ontrol and abortion is, itself, an unwritten right derived from fundamental beliefs about human liberty and dignity. Most Americans agree on the broad rights to which they are entitled - liberty, equality, due process, privacy, the enjoyment of property, family sanctity, representative government. While some of those rights are specifically stated in the Constitution, some are implied, and others only hinted at. And the scope of even such enumerated rights as "liberty" and "equal protection" is not self-evident, but can be defined only with reference to various wellsprings of meaning in the American experience. The full panoply of American rights cannot be derived exclusively from words on parchments. No more, however, should they be mined from expeditions into modern philosophy and psychology. There are intellectually principled ways in which American rights, even if unwritten, can be articulated from a study of America's constitutional writings and tradition.