JESSE U. LUCAS vs. JESUS S. LUCAS
G.R. No. 90710, June 6, 2011
“x x x.
We need not belabor the issues on whether lack of jurisdiction was raised before the CA, whether the court acquired jurisdiction over the person of respondent, or whether respondent waived his right to the service of summons. We find that the primordial issue here is actually whether it was necessary, in the first place, to serve summons on respondent for the court to acquire jurisdiction over the case. In other words, was the service of summons jurisdictional? The answer to this question depends on the nature of petitioner’s action, that is, whether it is an action in personam, in rem, or quasi in rem.
An action in personam is lodged against a person based on personal liability; an action in rem is directed against the thing itself instead of the person; while an action quasi in rem names a person as defendant, but its object is to subject that person’s interest in a property to a corresponding lien or obligation. A petition directed against the “thing” itself or the res, which concerns the status of a person, like a petition for adoption, annulment of marriage, or correction of entries in the birth certificate, is an action in rem.
In an action in personam, jurisdiction over the person of the defendant is necessary for the court to validly try and decide the case. In a proceeding in rem or quasi in rem, jurisdiction over the person of the defendant is not a prerequisite to confer jurisdiction on the court, provided that the latter has jurisdiction over the res. Jurisdiction over the res is acquired either (a) by the seizure of the property under legal process, whereby it is brought into actual custody of the law, or (b) as a result of the institution of legal proceedings, in which the power of the court is recognized and made effective. 
The herein petition to establish illegitimate filiation is an action in rem. By the simple filing of the petition to establish illegitimate filiation before the RTC, which undoubtedly had jurisdiction over the subject matter of the petition, the latter thereby acquired jurisdiction over the case. An in rem proceeding is validated essentially through publication. Publication is notice to the whole world that the proceeding has for its object to bar indefinitely all who might be minded to make an objection of any sort to the right sought to be established. Through publication, all interested parties are deemed notified of the petition.
If at all, service of summons or notice is made to the defendant, it is not for the purpose of vesting the court with jurisdiction, but merely for satisfying the due process requirements. This is but proper in order to afford the person concerned the opportunity to protect his interest if he so chooses. Hence, failure to serve summons will not deprive the court of its jurisdiction to try and decide the case. In such a case, the lack of summons may be excused where it is determined that the adverse party had, in fact, the opportunity to file his opposition, as in this case. We find that the due process requirement with respect to respondent has been satisfied, considering that he has participated in the proceedings in this case and he has the opportunity to file his opposition to the petition to establish filiation.
X x x.”