Issue Preclusion in Repeat Patent Cases

Blonder-Tongue Labs., Inc. v. Univ. of Ill. Found., 402 U.S. 313 (1971) involves a case where the patentee (University of Illinois) had first asserted its patent against Winegard and lost a bench trial on obviousness grounds. Later, the University sued Blonder, but the Supreme Court found the University’s case barred by collateral estoppel (AKA issue preclusion). Prior to this case the general rule was that collateral estoppel did not apply non-mutually – i.e., where the defendant in the second case was not part of the first case.

What should happen in the following situation?:

1. Assume that a patentee believes its rights are being infringed by a number of companies.

2. Patentee sues D1 for infringement; D1 raises prior art and challenges the patent as obvious; but Patentee wins, including a holding that confirms patent validity.

3. Patentee sues D2 for infringement; D2 raises the same prior art and obviousness argument; but Patentee wins, including a holding that confirms patent validity.

4. Patentee sues D3 for infringement; D3 raises the same prior art and obviousness argument; but Patentee wins, including a holding that confirms patent validity.

5. Next, Patentee sues D4 for infringement; D4 raises the same prior art and obviousness argument; However this time the patentee loses and the court holds the patent invalid as obvious.

6. Finally, Patentee sues D5 for infringement.

Question – Does D5 have the right to win the case on collateral estoppel grounds?

= = = =

[More Context]

I started thinking about this issue when reading the Restatement of the Law 2d – Judgments. Section 29 considers non-mutual issue preclusion and indicates that “other circumstances [may] justify affording [a would-be precluded party] an opportunity to relitigate the issue. The circumstances to which considerations should be given include those enumerated in § 28 and also whether . . . (4) The determination relied on as preclusive was itself inconsistent with another determination of the same issue.” The notes following §29 suggest two prior inconsistent outcomes “may have been based on equally reasonable resolutions of doubt as to the probative strength of the evidence or the appropriate application of a legal rule to the evidence. That such a doubtful determination has been given effect in the action in which it was reached does not require that it be given effect against the party in litigation against another adversary.”

Don Chisum emailed with two particular patent cases on point from his treatise. Mississippi Chem. Corp. v. Swift Agricultural Chem. Corp., 717 F.2d 1374 (Fed. Cir. 1983) and Stevenson v. Sears, Roebuck & Co., 713 F.2d 705 (Fed. Cir. 1983). In Mississippi Chem, the Federal Circuit held that prior inconsistent judgments serve as a “red flag warning” for the court to more carefully consider whether the patentee had a full and fair opportunity to litigate the issue in the case that resulted a finding of invalidity. The idea of this red-flag warning comes from a pre-Federal Circuit decision by the Fifth Circuit. Blumcraft of Pittsburgh v. Kawneer Co., 482 F.2d 542 (5th Cir.1973). In Blumcraft, the court wrote (in dicta) that “under our ruling today it would be technically possible to apply collateral estoppel where a prior finding of invalidity was preceded by several rather than by just one finding of validity.”

In such instances there would be a red flag warning a court to apply the full and fair criteria very carefully to determine if the court finding the patent invalid had adequately comprehended and applied the appropriate substantive standards.

In Blumcraft, the court described the Blonder-Tongue ruling as follows: “Blonder-Tongue did not throw merely a jab at the multiplicity of patent litigation; rather, it intended a knockout blow through the doctrine of collateral estoppel so that any time a patent was found invalid in a fair fight with a knowledgeable referee, the courts could count ten and the patent holder could no longer maintain that he was champion.” As it did in Mississippi Chem., the Federal Circuit followed this same approach in Stevenson.

72 thoughts on “Issue Preclusion in Repeat Patent Cases

  1. 72

    “[C]ollateral estoppel may be employed to preclude the relitigation of issues only when those issues were ‘actually litigated’ in a prior law suit. . . . When judgment is issued as the result of a default, however, the underlying issues have not been actually litigated. For that reason, a default judgment cannot serve to preclude the litigation of issues under the doctrine of collateral estoppel.” Farah v. Pramil S.R.L., 300 Fed.Appx. 915, 918 (Fed. Cir. 2008) (internal quotations omitted); see also Lee by Lee v. U.S., 124 F.3d 1291 (Fed. Cir. 1997) (same).

    Interestingly, from a quick review, the court in this case appears to have entered default on non-infringement only, refusing to do so on invalidity because of this very issue – 155030 Canada, Inc. v. Magnet 4U Co., Ltd., 2006 WL 543993 (D.D.C. 2006).

    See also Artmatic USA Cosmetics, a Div. of Arthur Matney Co., Inc. v. Maybelline Co., 906 F.Supp. 850 (E.D.N.Y. 1995) (refusing to apply collateral estoppel in these circumstances).

  2. 71

    Do courts actually confirm validity? I thought that they just find that the accused infringer failed to meets its burden to establish invalidity.

  3. 70


    An FYI: The Fifth Circuit Blumcraft case you cite (Blumcraft of Pittsburgh v. Kawneer Co., 482 F.2d 542 (5th Cir.1973)) was been criticized in a 1974 case note article which I cited in my appellant’s brief I submitted in the 1977 Giles Rich moot court competition. See “After Blonder-Tongue: Back to the Laboratory to Find a Patent Validation System Even a Court Could Trust,” 16 Wm. & Mary L. Rev. 295, 319 (1974).

  4. 68

    Didn’t I mention the infringers counterclaiming for invalidity?

    Yes, I thought that sounded strange. They’re counterclaiming for invalidity in each of the half-dozen individual ongoing suits that you filed, maybe even in different districts, in which you explicitly take the position that your patent is valid, and now you want to join them all in a completely separate action solely on the question of validity?

    Don’t you think you should maybe defend the validity of your patent in the same actions where you’ve asserted your patent and the defendant has raised the counterclaim of invalidity?

  5. 66

    Please explain (case or controversy – how is suing for a declaration [for which a presumption already exists] anything but a pure advisory action that Article III courts cannot provide?).

  6. 65

    Due to the new joinder rule, one can no longer sue for infringement numbers of unrelated defendants to force a common trial on validity. But consider this, if one sues a number of defendants in different cases, and they all counterclaim for invalidity, why can’t one sue all of them in one action for declaration that the patent is not invalid?

  7. 61

    Malcolm, we have class actions all the time that bind non parties who do not opt out. I don’t know why in principle a class of accused infringers could not maintain such a class action DJ against a patent owner.

    But charged defendants will not do that as it is their objective to force the PO to litigate the same issue again and again and again. I don’t think this is required by due process. All that is required is notice and the opportunity to be heard.

  8. 60

    And as for “troll boy,” must I remind you of your own self-defeat and the math which showed by a huge margin that you troll me?

    You seem to have an unnatural affinity for Malcolm’s peculiarities…

    Are you related to Francis?

  9. 59

    Number 1 on my list of the all-time best.

    Noted. I’ve still got books from last summer that need finishing!

  10. 58

    Exactly my point, Leopold, you simply pulled the ‘royal’ Malcolm sniff test maneuver and declared “It must be so!”

    And you are welcome.

  11. 57

    See, the Richards case below.

    Privity is a special situation.

    This is basic Civ Pro stuff, Ned. Absent some pretty clear-cut and rare exceptions, if you’re not a party to a patent case, you’re not bound by the judgement.

    This is a good thing, at least from the perspective of a citizen who prefers that laws which restrict his/her behavior be drafted by accountable legislators rather than “negotiated” between a government clerk and a corporate patent attorney.

  12. 56

    Malcolm, very true. But, still, it has to litigate the very same issue multiple times against a class of similarly situated defendants.

    See, the Richards case below. I think the SC may authorize offensive collateral estoppel if there is a strong invalidity case put up by an earlier litigant, and the non party to be bound is on notice and has an opportunity to join but chooses to stay on the sidelines. Perhaps the first court could give them notice that they can join and if they do not, they will be bound by the outcome. There would be no unfairness in that case. Due process will be satisfied.

  13. 55

    There are cases where non parties are bound by the outcome of other litigation where the issues are common, where the first case was adequately prosecuted, and where the party bound is on notice and has an opportunity to be heard.

    Richards v. Jefferson County, 517 U.S. 793, 798, 116 S.Ct. 1761, 135 L.Ed.2d 76 (1996). In Richard, the SC said this:

    Of course, these principles do not always require one to have been a party to a judgment in order to be bound by it. Most notably, there is an exception when it can be said that there is “privity” between a party to the second case and a party who is bound by an earlier judgment. For example, a judgment that is binding on a guardian or trustee may also bind the ward or the beneficiaries of a trust. Moreover, although there are clearly constitutional limits on the “privity” exception, the term “privity” is now used to describe various relationships between litigants that would not have come within the traditional definition of that term. See generally Restatement (Second) of Judgments, ch. 4 (1980) (Parties and Other Persons Affected by Judgments).

    In addition, as we explained in Wilks:

    “We have recognized an exception to the general rule when, in certain limited circumstances, a person, although not a party, has his interests adequately represented by someone with the same interests who is a party. See Hansberry v. Lee, 311 U. S. 32, 41-42 (1940) 799*799 (`class’ or `representative’ suits); Fed. Rule Civ. Proc. 23 (same); Montana v. United States, 440 U. S. 147, 154-155 (1979) (control of litigation on behalf of one of the parties in the litigation)….

    Richards further remarked,

    “Even assuming that our opinion in Hansberry may be read to leave open the possibility that in some class suits adequate representation might cure a lack of notice, but cf., id., at 40; Eisen v. Carlisle & Jacquelin, 417 U. S. 156, 177 (1974); Mullane v. Central Hanover Bank & Trust Co., 339 U. S., at 319, it may not be read to permit the application of res judicata here. Our opinion explained that a prior proceeding, to have binding effect on absent parties, would at least have to be “so devised and applied as to insure that those present are of the same class as those absent and that the litigation is so conducted as to insure the full and fair consideration of the common issue.”

  14. 54

    Here I think Faulkner was wrong. Absalom, Absalom! would not have been written if Faulkner hadn’t done it. Number 1 on my list of the all-time best.

  15. 53

    the PO should not be faced with multiple trials on the very same issue

    If it’s really so troublesome to re-litigate its patent, perhaps the PO should reconsider its IP protection and enforcement strategy.

    To the extent an issue in a second trial is the “same” as an issue successfully litigated in an earlier trial, the patent owner has a great advantage over the second defendant: experience litigating that identical issue, including all of the background research and back-up plans that went into the previous war.

  16. 51

    As long as the D3 suit is truly over and done with (i.e., no appeals pending, no pending lower court action, etc.), D3 has no cause of action or even any ability to overturn the injunction

    Correct me if I’m wrong, but I believe the lawyers and jurists who draft these injunctions are typically careful to note that the injunction ends on the date that the patent expires or is otherwise rendered invalid/unenforceable. Failure to observe that little nicety could render the injunction itself unenforceable.

  17. 50

    anon, I know that congress requires separate cases, but still the PO should not be faced with multiple trials on the very same issue. Given Bloner-Tongue, that is, IMHO,

    extremely anti-patent. Extremely.

    I remark that the ITC allows only one trial. The action is in rem.

    Perhaps that is the clue. We need statutory reform where validity litigation is “in rem” in some fashion.

  18. 48

    I wonder what Faulkner would think about his heirs grifting off his art in such a manner:

    If I had not existed, someone else would have written me, Hemingway, Dostoevsky, all of us. Proof of that is that there are about three candidates for the authorship of Shakespeare’s plays. But what is important is



      A Midsummer Night’s Dream

    , not who wrote them, but that somebody did. The artist is of no importance.

    — Paris Review interview (1958)

  19. 47

    Your pet vacuous posts are no answer, Malcolm.

    You really don’t get this ‘answer’ thing, do you?

  20. 46

    In the film, the Wilson character says: “The past is not dead. Actually, it’s not even past. You know who said that? Faulkner. And he was right.”

    In “Requiem for a Nun,” the Faulkner passage reads: “The past is never dead. It’s not even past.”

    Sony claims the quote is “fair use,”

    Maybe the only thing worse than having to give gratitude constantly is having to accept it.

    You’re welcome.

  21. 45

    faces with multiple, unrelated defendants, it needs to sue all of them, and then have the validity issue tried in one trial

    Rather difficult to entertain that notion, Ned – given the opposite direction as mandated by the AIA.

  22. 44

    Surely this is fair use

    Please don’t embarrass yourself with such a sloppy Fair Use analysis.

  23. 42


    Good insight on exception (2) being a possible basis for lifting an ongoing injunction. As injunctions are an “equitable” remedy, it would seem odd to not permit the defendants in the D1, D2, and D3 suits to be able to lift that injunction given that the reason for granting it (i.e., a valid patent) is no longer true. But a damages award (a remedy at “law”) is a past, “one time” deal without ongoing effects like an ongoing injunction.

  24. 41

    If the PO is faces with multiple, unrelated defendants, it needs to sue all of them, and then have the validity issue tried in one trial. Such is the way it is done in the ITC.

    While due process allows every defendant a defense, it does not require every defendant have a separate defense on common issues of law and fact.

  25. 40

    I couldn’t find any cases either, EG. I did find some different formulations of the exceptions, but not hugely different.

    (2) might also give grounds for lifting the injunction, especially if the patentee appealed the invalidity ruling and lost. In that case, a “controlling authority” would have sustained the invalidity, which sounds like a “subsequent contrary view of the law” to me.

    I agree with you regarding damages. The past is past in such a situation, regardless of what Faulkner said.

    Speaking of Faulkner, I was surprised to see that this case is still pending:
    link to
    Surely this is fair use. Making reference to earlier art and literature is one of the oldest literary and artistic traditions.

  26. 39

    You still have not provided a basis for your assumption.

    I know this “giving answers” thing is not something you are used to, so I will cut you a little slack.

  27. 38


    You raise an interestng point about the continued enforceability of an injunction against D3 (or that matter D1 or D2). Admittedly, I’m taking this from Wikipedia (which cites to Hanover Ins. Co.,105 F.3d at 312), which says that the law of the case doctrine precludes reconsideration of a previously decided issue unless one of three “exceptional circumstances” exists: (1) when substantially different evidence is raised at a subsequent trial; (2) when a subsequent contrary view of the law is decided by the controlling authority; or (3) when a decision is clearly erroneous and would work a manifest injustice. Either (1) or more likely (3) would suggest that an injunction against D1, D2 or D3 could be lifted in view of the subsequent invalidity ruling in the D4 suit. I think it’s more problematic whether any damage award would be rescinded as, while the injunction is ongoing, the damage award is essentially a “one time event.” And I know of no case, including the ones I cited above, that involved going back to the earlier cases to lift an ongoing injunction,

  28. 37

    That does not tell me the basis of your assumption.

    Here on planet Earth, Federal court decisions (including decisions regarding patent validity) are occasionally appealed to the Supreme Court.

    regarding spin: that is some horrible spin of your own

    Calm down, Trollboy.

  29. 36

    That does not tell me the basis of your assumption.

    And regarding spin: that is some horrible spin of your own to try to justify your incessant and reckless spin and mistreatment of facts and law.

    D- for effort.

  30. 35

    Why would you assume such?

    Dennis’ hypothetical is set up to present Blonder-Tongue as somehow unfair to patentees or at least as a counter-intuitive decision (“so many courts have upheld the validity of the patent that the court’s finding of invalidity in (5) shouldn’t have preclusive effect!!”). Nothing wrong with that, by the way. He’s putting some spin on the discussion. He’s entitled to do that.

    The hypothetical “plays out” a bit differently, I think, if you include between (5) and (6) the fact that the patentee either voluntarily chose not to pursue an appeal or appealed the case all the way to the Supreme Court and lost.

  31. 33

    If someone files a declaratory judgment action against a patentee and wins a default judgment of invalidity (because the patentee fails to respond). In that case, the patent should not be seen as invalid with respect to other parties, right?

    Of course it should, for the reasons that IANAE gave.

  32. 32

    What makes you call this an invalid patent?

    A very well-reasoned Supreme Court case.

    Your hypothetical doesn’t indicate what happened between (5) and (6). I assume the patentee appealed the invalidity finding to the Supreme Court and lost.

  33. 31

    So after D4 wins, Patentee cannot enforce the judgments (e.g., injunctions or damages) against D1, D2, and D3?

  34. 30


    And in the real world, when the party against which the injunction was issued in D3 notes the further developments and says – screw that injunction, let’s get back to making that thing – what happens next?

    Do you think a court (in equity and law) will enforce the injunction on a (later determined) invalid patent? Can the patentee in good faith bring a new action in the court to attempt to enforce the injunction, knowing the patent to be no longer valid? Isn’t that in itself inequitable conduct?

    As has been mentioned, the patent, once invalidated, is dead to the world (and that world still does include the earlier defendants). So while, technically true that the “law of the case” doctrine draws a line in the sand, the fact that the patent is invalid against the entire world is like a tsunami to that line, no?

  35. 29


    Most likely, the new D1 suit would result in Blonder-Tongue type collateral estoppel being applied and the patent claim(s) held invalid being deemed nonassertable in the new D1 suit. The basic proposition of Blonder-Tongue type collateral estoppel is the same: once you lose on patent validity of the relevant claim(s), that becomes preclusive on the validity issue for all subsequent suits involving the validity the same patent claim(s).

  36. 28


    As long as the D3 suit is truly over and done with (i.e., no appeals pending, no pending lower court action, etc.), D3 has no cause of action or even any ability to overturn the injunction or any damage award; I believe that’s covered by the “law of the case” doctrine. Blonder-Tongue doesn’t affect the earlier suits (i.e., D1 through D3), only the later suits (i.e., D4 through D5).

  37. 27

    “to the evil”‘s analysis, combined with WCG’s analysis and conclusion, I think wins the day.

  38. 26

    I don’t think there’s anything “wrongful” about the injunction. D3 failed to prove its case.

    I don’t see how D3 has a cause of action against the patentee. I’m not a civil procedure expert by any means, but I would guess that the court that granted the injunction retains jurisdiction over the matter so long as the injunction is in place, so D3 should petition the court for relief.

  39. 24

    If the above assessment is right, it seems to me the more difficult question is this one. Assume at Step 4 that D3 has been enjoined from manufacturing. After Step 5, does D3 have a cause of action against Patentee for the now-determined-wrongful injunction?

  40. 23

    Maybe this is illustrative of my ignorance of US law, but isn’t a declaratory judgment of *in*validity an in rem determination? It is in Canada and the UK (and, I would guess, Australia, NZ, etc.). If that is the case, there is no issue of ‘preclusion’. The patent has ceased to exist against the world.

    The converse does not apply, as other posters have noted. A failed invalidity attack only precludes the same party from litigating that issue. Although this might be argued to simply be a matter of failed “burden of proof”, the substantive policy reason is that invalid patents are a public mischief.

  41. 22

    Yes, those are mere “invalidity not proven” prior decisions, and furthermore “raises the same prior art and obviousness argument” does not mean using the same expert witnesses, etc. Also, an in rem proven INvalidity decision is not the same as precluding anyone else from even trying to prove invalidity. And in the real world [vis a vis academic debates] a 5th party sued on the same patent successfully sued on 4 times before would be brainless not to settle, file a reexamination or IPR, and make new combined-references arguments, not just proceed make the identical jury arguments of the prior losers.

  42. 21


    You’re most welcome. Lucky I kept my moot court briefs as it would have been more difficult to “reconstruct” the case law.

  43. 20


    I agree with IANAE. Blonder-Tongue type collateral estoppel focuses solely on whether the patentee had (or could have had) the opportunity to present their case on the validity issue. The fact that patent invalidity results due to a default judgment in a DJ action (provided the patentee could have presented their case on validity) shouldn’t matter.

  44. 18

    If someone files a declaratory judgment action against a patentee and wins a default judgment of invalidity (because the patentee fails to respond).

    On the premise that issue preclusion is about having had the opportunity, whether or not you made the most of it, my guess is that the patentee should be precluded from asserting the patent against other parties.

  45. 17

    Sorry to attempt to divert the hypothetical, but what if 6 is changed as follows.

    6. Next, Patentee sues D1 again for infringement of the same patent by a totally different product line; D1 raises the same prior art that D4 used to invalidate the patent but with which D1 was not able to prove invalidity during the first trial.

  46. 16

    If someone files a declaratory judgment action against a patentee and wins a default judgment of invalidity (because the patentee fails to respond). In that case, the patent should not be seen as invalid with respect to other parties, right?

  47. 14

    it only applies when the party being precluded was a party to the prior lawsuit as well.

    Right. As soon as the patentee (who is a party to all these suits) has a finding of invalidity, he’s precluded from arguing validity of the same claims in a subsequent action.

    Each of defendants D2, D3, D4 can always claim that the last guy didn’t argue the point properly, which isn’t their fault, so they get another shot at it.

  48. 13

    I should also note that it doesn’t matter that the same patent claims held invalid in the D4 suit were held valid in the D1 through D3 suits. One of the pre-Federal Circuit cases I cite had essentially that situation, and ruled that a prior ruling of validity would not preclude application of Blonder-Tongue collateral estoppel if there was subsequent ruling of invalidity. The Federal Circuit Pharmacia & Upjohn case I cite doesn’t directly address the valid first but later invalid scenario that is presented here, but I’m willing to bet that the D5 suit would nonetheless be barred by collateral estoppel as its one invalidity ruling only (no matter how many prior validity rulings )that matters.

  49. 12


    I’ll declare myself to be a “ringer” beforehand as this very question was part of a Giles Rich Moot Court Competition I participated in the year of 1977 (Dexter Paulsen v. Beta Company). Prior to the Federal Circuit’s creation in 1982, answer would be that D5’s suit would most likely be barred under Blonder-Tongue collateral estoppel, at least as to any patent claim that had been invalid in the D4 suit. See Bourns, Inc. v. Allen-Bradley Co., 480 F.2d 123, 125 (7th Cir. 1973)(only as to adjudicated claims); West Chemicals, Inc. v. Molded Fiber Glass Body Co., 498 F.2d 1115, 1117 (6th Cir. 1974), affirming 380 F.Supp. 517 (N.D. Ohio 1973) (also applicable to unadjudicated claims); Westwood Chemicals, Inc. v. U.S., 525 F.2d 1367, 1372 (Ct. Cl. 1975) (also applicable to unadjudicated claims); Bourns, Inc. v. U.S., 537 F.2d 486, 491-92 (Ct. C. 1975) (also applicable to unadjudicated claims); Technograph Printed Circuits, Ltd v. Emthoe Electronics, Inc., 484 F.2d 905, 908-9 (7th Cir. 1973)(ambiguous as to whether also applicable to unadjudicated claims). See also Smith, “The Collateral Estoppel Effect of a Prior Judgment of Patent Invalidity: Blonder-Tongue Revisited (Part II),” 55 JPOS 363 (1973). And yes I still have my Moot Court briefs I had to write for both sides!

    After the creation of the Federal Circuit 1982, Blonder-Tongue type collateral estoppel is still applicable. See Pharmacia & Upjohn Co. v. Mylan Pharmaceuticals, Inc., 170 F.3d 1373 (Fed. Cir. 1999)(patentee collaterally estopped by judgment of invalidity and unenforceability in earlier case involving same patent). So again, if we’re talking the same patent claims that were invalidated in the D4 suit, the D5 suit is most likely precluded by Blonder-Tongue type collateral estoppel under current Federal Circuit case law precedent.

  50. 9

    Preclusion does not work both ways. Rather, it only applies when the party being precluded was a party to the prior lawsuit as well. The idea is that each party should get their day in court.

  51. 8

    Corrected… Why can D2, D3, and D4 raise an obviousness objection using the same art in the first place if it was already decided in D1? Should not preclusion work both ways?

  52. 6

    D5 certainly has a defense relating to unenforceability of a judicially-determined invalid patent; however, I don’t see how collateral estoppel can be sustained. Since a patent has a presumption of validity, a court does not make a finding of validity; rather, the court can make a finding of invalidity. A legal issue of validity should never be raised by the patentee because of the presumption, and because the issue of validity has never been addressed by the court, there is no issue from which the patentee is precluded.

  53. 5

    If there is preclusion, why can D5 raise obviousness using the same art in the first place? Should not preclusion work both ways?

  54. 4

    Not sure what’s bothering you here. In the first three cases the determination would have been that the patent was not invalid, i.e. that the defendants had not shown by clear and convincing evidence that the patent was invalid. That’s not the same as a determination of validity, which in practice can’t be made (since the court can’t possibly review everything ever known to man before the patentee invented the claimed invention, and therefore the court limits its scope of inquiry to the prior art profferred by the defendant). The patent is presumed valid b/c you can’t prove validity, you can only parry an assertion of invalidity. What SCOTUS was saying in Blonder was that the validity will be always be subject to attack, even on the basis of prior art used by someone else in a previous trial, because the new defendant is entitled to put on a defense of its choosing and can’t be precluded from attacking the validity using prior art of its choosing, simply because an earlier defendant wasn’t able to make out a convincing case using the same prior art. But once the patent has been determined to be invalid, there’s nothing left to prove. So the answer to your hypothetical is, of course the suit against D5 should be precluded and D5 should win on collateral estoppel grounds.

    And I like Hedley (that’s Hedlee!)’s question above. (Here’s the link for readers who are too young to get the reference: link to

  55. 3

    It’s been 40+ years since Blonder-Tongue was decided. This hasn’t been resolved yet?
    IIRC, the consensus in law school two years after the decision was that the patentee can keep suing until he loses on validity, after that: too bad, so sad.

    No rationality — simply public policy regarding patents.

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