Zygmunt Ziembiński was one of the most prominent theoreticians of law in Poland in the second half of the 20th century. He developed an original theory of law defined as a theory of legal phenomena, which covered both logical-linguistic as well as real aspects of law. The theory served as a base for the development of a unique so-called advanced normative conception of sources of law, one of the greatest achievements of theory of law in Poland. This conception encompasses all the indispensable elements of a coherent system of binding legal norms: 1) indication of a political justification (ideological assumptions) of the entire system of law; 2) pre judgment of law-making competence of government agencies; 3) determination of the status of custom and precedent; 4) compilation of a catalogue of permissible interpretation rules; 5) compilation of a catalogue of permissible inferential rules (permissible rules of legal inferences); 6) compilation of a catalogue of permissible collision rules.