The present work addresses the issue of the prevalence of instrumentality in the study of Brazilian tax law, which reduces its field of study through the anachronistic adoption of strict positivism. By analyzing the prevailing doctrine that drives this perspective in the study of law, a phenomenological framework of taxation is presented, which urgently calls for answers from tax law, especially regarding the integration of law in postmodernity. In perspective, the context of the Brazilian tax matrix is considered, which presents challenges that are ignored by the definition of the field of study of tax law insofar as the dominant positivism limits itself to analyzing the norm in its semantic bias, disregarding the efficacy and the social, political, and economic context in which it is inserted. Moreover, it is also demonstrated in this work that the deductive philosophical foundation adopted by Brazilian strict tax positivism does not bring novelty to the field of taxation, limiting itself to seeking legal certainty as a value element for closing its formalistic logical circuit. The present study aims to criticize this position of the doctrine by asserting that strict positivism, besides being unable to achieve the creation of the definitive methodology it so desires, also creates an epistemological break that limits the understanding of law as mere instrumentalization of domination and power.