The basic categories of Brazilian Civil Law face changes that foster the promotion of freedoms in diverse fields.This study stems from this assumption to assess grounds for decision-making in Family Law, chiefly when indeterminate normative texts -as the best interest of the child -are at stake, while stressing controllability issues derived from intentional indeterminacy.Due to the condition of developing persons, substantive freedom is demonstrated to play a pivotal role in defining the functions of family and the constraints they pose upon coherent and stabilizing decision-making.