This article has as general goal to find parameters in order to determine when the judicial activism leaves the field of legal argumentation and becomes an instrument of political decision. To this end, we started trying to define a possible concept of judicial activism and its origins in the United States juridical tradition. In this first moment, we use the historical analytical method to try to contextualize historically the conceptual categories under study and the conditions of emergence of this phenomenon in the United States. Following, on the basis of the critical comparative method, we began to study the fundamental elements that characterize political rationality and legal rationality. At the end, we discuss the prospects for an activist judge in Brazil, especially when acting in the protection of fundamental rights and ensuring the supremacy of the constitution. In general terms, our conclusions points to a set of criteria for the definition of what would be a so-called positive judicial activism, to the detriment of its other sort that is harmful to the wealth of the constitutional order.
Constitutional law; legal decision; political decision, legal argumentation; judicial activism