  The well-known debate about the sources of law appears to be radically undercut by a view of law as ideology. The sources debate has usually been posed in terms of the extent to which morality is intrinsic to the definition of law. Natural lawyers argue that what is law must partly depend on moral criteria. Following Thomas Aquinas, the traditional criteria have not strayed far from the teachings of the Roman Catholic Church, but more recent natural law arguments, such as those of Lon Fuller and Ronald Dworkin, have proffered secular standards emanating from the procedural ideals of the rule of law or the constitutionalism of American liberalism. All natural lawyers, however, are agreed that what the law is must be determined, in some sense, by what the law ought to be.