This Chapter examines the rules that prevent re-litigation of claims and issues that have already been contested (or, in some situations, could have been contested) in an earlier lawsuit. The most important concepts in this Chapter are:
“Res judicata”: There is a set of rules that prevents re-litigation of claims and issues; the set is sometimes collectively called the doctrine of “res judicata.” There are two main categories of rules governing re-litigation: the rules of “claim preclusion” and the rules of “collateral estoppel.”
Claim preclusion: The rules of “claim preclusion” prevent a claim (or “cause of action”) from being re-litigated. They break down into two sub-rules:
Merger: Under the rule of “merger,” if P wins the first action, his claim is “merged” into his judgment. He cannot later sue the same D on the same cause of action for higher damages.
Bar: Under the doctrine of “bar,” if P loses his first action, his claim is extinguished, and he is barred from suing again on that cause of action.
Collateral estoppel: The rules of “collateral estoppel” prevent re-litigation of a particular issue of fact or law. When a particular issue of fact or law has been determined in one proceeding, then in a subsequent proceeding between the same parties, even on a different cause of action, each party is “collaterally estopped” from claiming that that issue should have been decided differently than it was in the first action. A synonym for “collateral estoppel” is “issue preclusion.”