LEGAL PRINCIPLE: CIVIL PROCEDURE – Estoppel per rem judicatam (Res Judicata) – Conditions for a Successful Plea

This principle reiterates the three essential elements required for res judicata to bar subsequent litigation. The doctrine prevents re-litigation of matters already finally determined between the same parties, serving the public interest in finality and preventing vexatious litigation. However, its application requires strict proof of three distinct elements: (1) Identity of parties—the litigants in both proceedings must be the same persons or their privies (legal successors, representatives, assigns, or others in privity of interest). Strangers to the first action cannot be bound by its outcome. (2) Identity of issues—the specific questions of law and fact decided in the first case must be identical to those raised in the second case. Similar or related issues are insufficient; the test is whether the same question was necessarily decided. (3) Identity of subject matter—the right, property, or relationship in dispute must be the same in both cases. Different aspects of the same general subject do not suffice; the specific matter adjudicated must be identical. All three elements must be proved cumulatively—absence of any one defeats the plea. The burden rests on the party pleading res judicata to establish each element. The requirement for strict identity reflects the doctrine’s serious consequence: complete bar to litigation. Courts carefully scrutinize claimed identities to ensure that only truly duplicative litigation is barred while legitimate claims involving different parties, issues, or subject matter proceed. This principle prevents overreach in applying res judicata while maintaining its core purpose of preventing endless re-litigation of identical disputes. The strict requirements protect litigants’ access to justice while preventing abuse through repetitive suits.