"x x x.
Customary international law has the same status as a statute enacted by Congress. Thus, it must not run afoul with the Constitution. Customary international law cannot validly amend the Constitution by adding another category of natural-born Filipino citizens, specifically by considering foundlings with no known parents as natural-born citizens. Again, under paragraphs (3) and ( 4) of Section 1, Article IV of the 193 5 Constitution, in relation to Sections 1 and 2, Article IV of the 1987 Constitution, only those born of Filipino fathers or Filipino mothers are considered natural-born Filipino citizens.
Applying customary international law to the present case, specifically the right of every human being to a nationality and the Philippines' obligation to grant citizenship to persons who would otherwise be stateless, a foundling may be naturalized as a Filipino citizen upon proper application for citizenship. This application should not be interpreted in the strictest sense of the word. On the contrary, the term "application" for purposes of acquiring citizenship must be construed liberally in order to facilitate the naturalization of foundlings. The application for citizenship may be any overt act which involves recognition by the Philippines that the foundling is indeed its citizen. Thus, the application for citizenship may be as simple as applying for a Philippine passport, which serves as evidence of citizenship. 78 x x x.
x x x.
Before a foundling is conferred Philippine citizenship, there must first be a factual determination of the child's status as a foundling after an administrative investigation. Once factually determined that a child is a foundling, that child through its guardian may thereafter initiate proceedings to apply for Philippine citizenship, e.g., apply for a Philippine passport.
This need for a factual determination prevents the foundling from automatically acquiring Philippine citizenship at birth. The fact of unknown parentage must first be proven in an administrative proceeding before a foundling is granted citizenship on account of the child's foundling status. Such factual determination is a necessary act to acquire Philippine citizenship, preventing the foundling from being a natural-born Filipino citizen. In contrast, for natural-born Filipino citizens, no factual determination in an administrative proceeding is required to grant citizenship since the certificate of live birth speaks for itself -it establishes natural-born citizenship.
x x x."
See -
SC.JUDICIARY.GOV.PH
