Short answer. That person is likely an indispensable party. Section 7 of Rule 3 requires that parties 'without whom no final determination can be had of an action' be joined as plaintiffs or defendants — without them, the court cannot fully and validly resolve the case.

What the law says

Parties in interest without whom no final determination can be had of an action shall be joined either as plaintiffs or defendants.

Rule 3, Section 7 — Compulsory joinder of indispensable parties. Read the full provision →

What makes a party indispensable

Section 7 defines indispensable parties functionally rather than by category: they are 'parties in interest without whom no final determination can be had of an action.' The test is whether the court can actually reach a complete, valid resolution of the dispute without that person's presence — not merely whether their presence would be convenient or helpful. If their absence would leave the judgment incomplete or ineffective as to the real controversy, they are indispensable. A common example is a co-owner of property, or a party to a contract whose rights would necessarily be affected by the judgment; if that person's interest is so intertwined with the relief sought that no judgment can settle the matter without also determining their rights, they belong in the case as an indispensable party, not merely an optional one.

Why joinder is compulsory, not optional

Unlike some other categories of parties, indispensable parties must be joined — the section frames it as a requirement, joining them 'either as plaintiffs or defendants,' depending on where their interest aligns. This reflects a basic due-process concern: a court generally should not adjudicate rights in a way that binds or vitally affects someone who was never given the chance to be heard in the proceeding, especially when no complete determination is even possible without them. This is different from a mere necessary party, whose absence does not prevent the court from deciding the case at all but only from granting complete relief; the compulsory joinder rule in Section 7 applies specifically to indispensable parties, and does not extend the same mandatory-joinder treatment to every party who simply has some interest in the outcome.

The practical consequence of leaving one out

When an indispensable party is missing, the usual course is for the court to require that party's inclusion before the case can move forward to a valid judgment, rather than proceeding to a decision that cannot fully settle the matter. This is why a court may flag the omission early and decline to proceed until the gap is filled — continuing without the indispensable party risks a judgment that fails to resolve the actual controversy for everyone whose rights are involved. A party who is simply not before the court is not automatically deprived of any right by the case's outcome; because they were never joined, a judgment rendered without them generally does not bind them, which is precisely why courts insist on their inclusion rather than allowing the case to proceed to a judgment that could not actually settle anything as to them.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.