opinion juris sive necessitates (opinion as to law or necessity).

Foundlings are likewise citizens under international law. Under the 1987 Constitution, an international law can become part of the sphere of domestic law either by transformation or incorporation. The transformation method requires that an international law be transformed into a domestic law through a constitutional mechanism such as local legislation.124 On the other hand, generally accepted principles of international law, by virtue of the incorporation clause of the Constitution, form part of the laws of the land even if they do not derive from treaty obligations. Generally accepted principles of international law include international custom as evidence of a general practice accepted as law, and general principles of law recognized by civilized nations.125 International customary rules are accepted as binding as a result from the combination of two elements: the established, widespread, and consistent practice on the part of States; and a psychological element known as the opinion juris sive necessitates (opinion as to law or necessity). Implicit in the latter element is a belief that the practice in question is rendered obligatory by the existence of a rule of law requiring it.126 "General principles of law recognized by civilized nations" are principles "established by a process of reasoning" or judicial logic, based on principles which are "basic to legal systems generally,"127 such as "general principles of equity, i.e., the general principles of fairness and justice," and the "general principle against discrimination" which is embodied in the "Universal Declaration of Human Rights, the International Covenant on Economic, Social and Cultural Rights, the International Convention on the Elimination of All Forms of Racial Discrimination, the Convention Against Discrimination in Education, the Convention (No. 111) Concerning Discrimination in Respect of Employment and Occupation."128 These are the same core principles which underlie the Philippine Constitution itself, as embodied in the due process and equal protection clauses of the Bill of Rights.129