Estoppel

The principle of “cause of action estoppel” prevented a party to an action from asserting or denying, as against the other party, the existence of a particular cause of action, the non-existence or existence of which had been determined by a court of competent jurisdiction in previous litigation between the same parties.

If the cause of action had been determined to exist, namely where judgment had been given upon it, it was said to have been merged in the judgment, or transit in rem judicatam. If it had been determined not to exist, the unsuccessful plaintiff could no longer assert that it did; he was estopped per rem judicatam.

The constituent elements in a case based on cause of action estoppel were that: (i) the decision, whether domestic or foreign, had been judicial in the relevant sense; (ii) it had in fact been pronounced; (iii) the tribunal had had jurisdiction over the parties and