LEGAL PRINCIPLE: EVIDENCE LAW – Estoppel Per Rem Judicatam – Requirements for Successful Plea of Res Judicata

This principle establishes the three essential elements that must be proved cumulatively for res judicata to apply. First, identity of parties: the parties in both proceedings must be the same persons or their privies (successors in interest, representatives, or those in privity). This prevents strangers to earlier litigation from being bound by judgments to which they were not parties. Second, identity of issues: the specific legal and factual questions decided in the earlier case must be identical to those raised in the current case. Similar or related issues are insufficient—the question must be the same (eadem quaestio). Third, identity of subject-matter: the property, right, or relationship that is the focus of both proceedings must be identical. The burden of proving these three elements rests on the party pleading res judicata. All three must be established; failure to prove any one element defeats the plea. The principle serves the public interest in finality of litigation while ensuring that only truly identical disputes are barred. Courts must carefully scrutinize each element: parties must be examined to verify true identity or privity; issues must be compared to ensure they are not merely similar but identical; and subject-matter must be shown to be the same property or right. The strict requirements prevent res judicata from being used as a blunt instrument to bar legitimate new claims while ensuring that definitively decided matters cannot be re-litigated.