Inside the Supreme Court

Petition to Decision

Papers of Supreme Court Justices on Civil Rights Cases

David Achtenberg

Professor & Law Foundation Scholar

UMKC School of Law

Kansas City, MO 64110-2499


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Preclusive Effect: A Quick and Dirty Explanation
Three of the cases discussed in Petition to Decision  (Allen, Migra, and McDonald) deal with the preclusive effect of prior litigation on subsequent litigation.  This subject (sometimes referred to as "preclusive effect" or "prior adjudication") is studied at length in law school Civil Procedure courses.  The following is a greatly simplified, "quick and dirty" explanation of the two most commonly discussed aspects of preclusive effect: Collateral Estoppel (also known as "Issue Preclusion") and Res Judicata (also known as "Claim Preclusion"). 

Under the doctrine of collateral estoppel a person who has lost on a legal or factual issue in one case generally cannot re-litigate the same issue in a second case.  For example, suppose Paul sues the manufacturer of a lawn mower for personal injuries claiming that the mower was dangerously defective.  If Paul loses because the court or jury finds that the mower was not defective, Paul is bound by that finding.  He cannot, for example, now assert that the design was defective in a suit against the store that sold him the mower.  If Paul has not yet paid for the mower and is sued by the store, he cannot assert that the mower was defective as a defense to that suit.  Having lost once on his contention that the mower was defective, Paul is barred ("estopped") from asserting that contention in future litigation, either as a claim or a defense. 

Under the doctrine of res judicata, a plaintiff who has various closely related claims against a defendant is required to join those claims in a single suit.  If the plaintiff does not do so, he or she will be barred from asserting the omitted claims in a subsequent suit against that defendant.  For example, suppose Penny Pedestrian is hit by Dan Driver and sues him for injuries to her arm.  Whether Penny wins or loses, she cannot subsequently sue Dan for injuries to her leg or for damage to the computer she carrying when she was hit.  If she won the first case, her omitted claims are said to be "merged" into the judgment she received.  If she lost the first case, her omitted claims are said to be "barred" by that judgment. 

The defenses of collateral estoppel and res judicata are much more complicated than this simplified explanation would suggest.  Each is subject to very significant exceptions and can only be asserted successfully if various elements are satisfied.  As is evident from the three cases, individual states (not to mention, the federal courts) interpret and apply the defenses differently.  I hope this quick and dirty explanation is helpful to you as you view this website.  If you are a law student, it is no substitute for studying the subject thoroughly in your classes.  If you are a layperson, it is no substitute for legal advice from an attorney licensed in the relevant jurisdiction.  If you are a lawyer, you already know more about these defenses than could possibly be summarized here.