Suppose you get sued by a patent troll. You then learn that the troll has been sitting on its patent for years without giving you any warning. If you’d known about the risk, you might have been able to design your product differently to avoid infringement. Even worse, when you try to prove that the patent covers an obvious invention, all of the best evidence (such as websites or code repositories) has disappeared because of the passage of time. Instead of winning the case, you must pay years worth of damages to the troll.

The legal doctrine of “laches” is supposed to shield defendants from this scenario. If a plaintiff simply sleeps on his rights and as a result harms the ability of a defendant to defend himself, courts can refuse to enforce the plaintiff’s legal claim. (This is different from a statute of limitations, which sets a fixed time limit for bringing suit but does not consider whether the plaintiff delayed suit to the detriment of the defendant). Last week, together with Public Knowledge, EFF submitted an amicus brief arguing that laches should apply in patent cases.

The case is called SCA Hygiene v. First Quality Baby Products, and it relates to a patent on adult diapers, something EFF usually wouldn’t get involved in. But we did here because the Federal Circuit (the court that hears almost all patent appeals) will decide whether laches continue to apply in patent cases. The court is considering this question because last year the Supreme Court decided the copyright case Petrella v. MGM. In Petrella, the Supreme Court said that laches did not apply to copyright cases. So the question: based on Petrella, should laches continue to apply in patent cases?

We think laches should still be available, and here’s why: patent defendants and copyright defendants are in very different positions when it comes to defending against stale claims. Patent defendants, unlike their copyright counterparts, often defend themselves by showing that the patent owner’s claimed invention was obvious at the time of filing (thus making the patent invalid). But by delaying a lawsuit, a patent owner can make it difficult for the defendant to find what was known back when the application was filed; records get lost through the passage of time.

This is particularly important in the Internet era and with software patents. Traditionally, patent defendants would rely on other patents or journal articles to show that an invention was not new. In a world where innovation is routinely described in patents or journal articles, the passage of time may not be much of a worry: the USPTO or the library might have a copy of the work. But in the Internet age, where innovation occurs rapidly and often without any thought of patents or journals, the best proof that something was already known is often not easy to find. Websites are constantly rewritten. Software code gets lost or is not documented. For the patent defendant, without “laches” it could be possible to lose even though what the patent owner claimed was not actually new. Patent owners, absent laches, would be able to assert invalid patents with impunity.

Laches should exist in patent law, despite the Supreme Court’s decision in Petrella, because this is a place where patent law and copyright law differ. We hope the Federal Circuit recognizes the important differences between copyright law and patent law, and how patent owners, by delaying, seriously impact the ability of an innocent defendant to invalidate bad patents.