Soft law or hard law? Quantitative evidence from the legalization of ASEAN instruments

ASEAN integration has commonly been understood as a paradigmatic case of intergovernmental institutional practice. However, as ASEAN’s normative framework has become increasingly elaborated, a growing body of scholarship has argued that ASEAN is gradually moving toward a rule-oriented model of regional governance. Existing studies have offered valuable theoretical interpretations and case-based analyses, but quantitative evidence remains limited. To address this gap, this article draws on the concept of “legalization” developed by Abbott et al. to code and analyze 1,273 ASEAN instruments, thereby revealing the characteristics and evolutionary logic of ASEAN’s institutionalization process. The findings show that the overall level of legalization follows a bimodal distribution and displays an asymmetric pattern across its three dimensions, characterized by “moderate precision, low obligation, and low delegation.” Diachronically, the 2008 entry into force of the ASEAN Charter marks a turning point, after which legalization exhibits nonlinear, stage-based fluctuations. Beta regression results further indicate that economic heterogeneity among member states and external economic openness are positively associated with legalization, whereas domestic political uncertainty is negatively associated with it. These results suggest that ASEAN’s institutionalization is the outcome of a continuous and dynamic trade-off among member states between deepening regional cooperation and preserving national sovereignty.