Application of Natural Law Doctrine in Constitutional Court Decision No. 20/2564

In late 2021, the Constitutional Court of Thailand issued a decision concerning the constitutionality of Section 1448 of the Thai Civil and Commercial Code. Due to the decision, same-sex marriage remains unregulated. The Court implemented natural-law doctrines as their reasons. Natural-law theories are the primary opponents of same-sex marriage within the jurisprudential debate. This paper explores the natural-law doctrines used and presents an analysis of this constitutional decision by way of legal philosophy. Hume’s Law is helpful in discerning natural-law theories. The citation of Cicero’s “true law" proves to help analyse other doctrines and comment on some of the contradictions from the natural-law applications. One contradiction is the citation of Cicero’s text itself, another, from the simultaneous reference of nature and tradition. Another apparent reference of natural-law doctrines the Court used is the preservation argument. Upon the subjects of marriage, natural law, and procreation, it is worthy of exploring some of John Finnis’s natural-law theory and its similarity with this decision’s rationales. This constitutional decision is significant from the philosophical perspective and an excellent opportunity to explore the role of the legal philosophy of the ancient Greek to the contemporary period in Thai jurisprudence.