  One variant of hybrid interpretivism is the conception of law as consisting of both rules and principles. This is typically attributed to Dworkin’s early work (Dworkin 1978; notice that Dworkin actually disowns this view: 1978, at 76). Institutions convey rules, as Hart claimed. These are screened and rejected or modified to the extent that they conflict with certain basic moral principles of fairness or justice, as they did in Riggs.  Rules are also supplemented with non-conflicting principles in hard cases, where the rules alone yield no determinate results. In such cases, the principles fill the gaps. The law is the hybrid of the two sets of standards generated by the filtering and gap-filling operation.