The doctrine of res judicata belongs to the realm of evidence. It is for the party who pleads it as a bar to establish it. Ordinarily, a litigant has a right to institute a suit or other proceedings at their sweet will where there exists a cause of action.
​The doctrine of res judicata means that a matter in issue which has been adjudicated on merits between the same parties—either actually or constructively—will bind them irrespective of whether the decision is right or wrong.
​To constitute res judicata, at least the following three ingredients must be satisfied:
​(a) Final adjudication by a competent court: That is to say, the court must have jurisdiction to adjudicate the dispute and must have adjudicated the entire controversy on facts and law, finally and authoritatively. The jurisdiction under Articles 226 and 32 of the Constitution is discretionary. The exercise of these jurisdictions does not ordinarily contemplate the adjudication of all causes of action or all rights, especially when such determination would involve disputed questions of fact and law. Since res judicata applies only to matters adjudicated on merits (actually or constructively), its application under Articles 226 and 32 is limited, as the entire lis is not ordinarily decided on merits in such proceedings.
​(b) Parties must be one and the same: The parties in the current proceedings must be the same as in the earlier proceedings. The doctrine does not apply where the parties are different. That is why a conviction in a criminal case is not even prima facie evidence in a civil proceeding.
​(c) Identical Cause of Action: The cause of action in the current proceedings and that in the earlier proceedings must be one and the same.
​(d) Adjudication on merits: The cause of action must have been finally adjudicated upon its merits. All bundles of causes of action and all rights arising inter se between the parties must have been fully adjudicated. This would include giving both parties a full opportunity to adduce evidence in support of their case, as well as to rebut the evidence appearing against them, either actually or constructively.
​From the above, it is manifest that the doctrine of res judicata applies with full force to cases adjudicated by civil courts, for civil courts are courts of record of plenary jurisdiction. However, res judicata does not apply with full force to Tribunals or forums of limited jurisdiction. Proceedings under Articles 226 and 32 do not involve a full-fledged trial on all causes of action between the parties regarding all inter se rights and obligations. The jurisdiction exercised is discretionary. Therefore, the denial of discretionary relief cannot operate as res judicata, as nothing was decided. There is no merger of the cause of action as there was no final adjudication on merits; the court merely declined its discretionary jurisdiction.
​Interlocutory orders, which do not involve the adjudication of rights or obligations on their merits, also do not constitute issue estoppel, much less cause of action estoppel or res judicata.
​These are all fundamental principles of law. However, there are widespread misconceptions regarding these principles. Certain judgments of the Supreme Court, even those of Constitution Benches, state that the doctrine of res judicata is applicable to proceedings under Articles 226 and 32 without any detailed discussion. This creates difficulties for lawyers practicing in High Courts and subordinate courts, because it is considered blasphemous to say that a Supreme Court judgment does not lay down the correct law.
​Res judicata, res inter alios acta, and the doctrine of merger have their origins in Roman law—specifically Justinian’s Digest and Julian’s Code. It is difficult to fully understand these principles without studying classical Roman law, which is not possible unless one familiarizes oneself with classical Latin.