Methodological assumptions underpinning Józef Nowacki’s research were one of the most original and intriguing aspects of his approach to legal theory. An extremely rigorous conception of what kind of legal claims may be regarded as scientific can be reconstructed based on his various writings about legal norms, general clauses, dispositive provisions of law, legal principles or the practical application of the constitutional notion of the rule of law. His relentless efforts to uncover and eliminate from scientific discourse any evaluative judgments served to defend legal theory against ideological influences and subjective wishful thinking disguised as scientific claims. In these respects, it not only was an unquestionably valuable position then, but it remains so nowadays. At the same time, it begs numerous questions and doubts that still permeate central methodological debates in jurisprudence.