Possible Bar Exam Question: A and B sued X. A judgment was rendered in their favor. It became final and executory. May A interpose/invoke res judicata if there is a suit filed by B against him? Why?
Answer to the question: No, because res judicata is applicable only as between those who were adverse parties in the former suit and not between co-parties, for the judgment therein ordinarily settles nothing as to the relative rights or liabilities of the co-plaintiffs or co-defendants inter se, unless their hostile or conflicting claims were actually brought in issue by cross-claim or separate and adverse answers. (Valdez vs Mendoza, 89 Phils. 83)