Constructivism is a concept rooted in Kantian interpretations of ethics, which the American philosopher John Rawls further developed and systematized in the foundation of principles of justice and his theory of “Justice as Fairness.” Moral constructivism holds that ethical principles are not independent, preexisting realities, but the product of rational agreement among moral agents within a hypothetical or idealized process. This study seeks, relying on Rawls’s formulation of constructivist theory, to examine the possibility of applying it to the analysis of issues in Islamic legal theory (Usul al-Fiqh). The research employs an analytical–conceptual and comparative approach. The findings indicate that certain foundational issues—such as the theory of approval (taṣvīb), assignment (ijā’), retraction from fatwā, and ijtihād in cases of blockage—can be interpreted constructivistically; that is, in these cases, the legal ruling is not a preexisting entity but depends on the rational process of ijtihād. The ultimate aim of the article is to open new horizons for intercultural dialogue between modern moral philosophy and the Islamic jurisprudential tradition.