"x x x.
The 1987 Philippine Constitution is clear: "No person may be elected President unless he is a natural-born citizen of the Philippines, x x x, and a resident of the Philippines for at least ten years immediately preceding such election." Is petitioner, being a foundling, a natural-born Filipino citizen?
The answer is clearly no. First, there is no Philippine law automatically conferring Philippine citizenship to a foundling at birth. Even if there were, such a law would only result in the foundling being a naturalized Filipino citizen, not a natural-born Filipino citizen.
Second, there is no legal presumption in favor of Philippine citizenship, whether natural-born or naturalized. Citizenship must be established as a matter of fact and any doubt is resolved against the person claiming Philippine citizenship.
Third, the letter and intent of the 1935 Constitution clearly excluded foundlings from being considered natural-born Filipino citizens. The Constitution adopts the }us sanguinis principle, and identifies natural-born Filipino citizens as only those whose fathers or mothers are Filipino citizens. Petitioner failed to prove that either her father or mother is a Filipino citizen.
Fourth, there is no treaty, customary international law or a general principle of international law granting automatically Philippine citizenship to a foundling at birth. Petitioner failed to prove that there is such a customary international law. At best, there exists a presumption that a foundling is domiciled, and born, in the country where the foundling is found.
Fifth, even assuming that there is a customary international law presuming that a foundling is a citizen of the country where the foundling is found, or is born to parents possessing the nationality of that country, such presumption cannot prevail over our Constitution since customary international law has the status merely of municipal statutory law. This means that customary international law is inferior to the Constitution, and must yield to the Constitution in case of conflict. Since the Constitution adopts the jus sanguinis principle, and identifies natural-born Filipino citizens as only those whose fathers or mothers are Filipino citizens, then petitioner must prove that either her father or mother is a Filipino citizen for her to be considered a natural-born Filipino citizen. Any international law which contravenes the jus sanguinis principle in the Constitution must of course be rejected.
Sixth, petitioner failed to discharge her burden to prove that she is a natural-born Filipino citizen. Being a foundling, she admitted that she does not know her biological parents, and therefore she cannot trace blood relation to a Filipino father or mother. Without credible and convincing evidence that petitioner's biological father or mother is a Filipino citizen, petitioner cannot be considered a natural-born Filipino citizen.
Seventh, a foundling has to perform an act, that is, prove his or her status as a foundling, to acquire Philippine citizenship. This being so, a foundling can only be deemed a naturalized Filipino citizen because the foundling has to perform an act to acquire Philippine citizenship. Since there is no Philippine law specifically governing the citizenship of foundlings, their citizenship is addressed by customary international law, namely: the right of every human being to a nationality, and the State's obligations to avoid statelessness and to facilitate the naturalization of foundlings.
x x x."