The kids are fighting over something and bring it to me to resolve. I don’t really want to get involved in whatever they’re arguing about, but instead of just telling them to knock it off, I agree to hear them out on one condition: if they’re going to drag me into this, they have to accept my decision and move on.
Each kid is convinced he’s absolutely right, so they agree. After listening to both number 1 and number 2’s arguments, I decide number 2 was wrong. I tell him that number 1 is right and that he needs to apologize. They both leave, number 1 looking smug and number 2 pouting.
Five minutes later, number 2 comes back and starts making the same arguments again, insisting I must not have understood the first time. I stop him right there and remind him that this issue has already been decided and he agreed to accept the judgment.
This is the basic legal principle of “issue preclusion”: once a court has finally decided a specific issue of fact or law, the parties can’t re-litigate that same issue in a later case- even if later case involves different claims.
Issue preclusion comes up frequently in patent cases because they often involve two sequential proceedings: an Inter Partes Review (IPR) at the Patent Trial and Appeal Board, followed by district court litigation. An IPR may cancel some claims, after which the patentee amends the lawsuit to assert similar—but not identical—claims in court. The accused infringer naturally argues that the PTAB has already decided the relevant issues and that the patentee should not get another bite at the apple.
The Federal Circuit has generally rejected that argument. Because invalidity in an IPR is decided under the lower preponderance of the evidence standard, while invalidity in district court must be proven by clear and convincing evidence, the two proceedings do not resolve the “same issue” for purposes of issue preclusion. In short, what counts as “already decided” in an IPR often isn’t “already decided” in court.
Number 2 would certainly approve.