EFF submitted an amicus brief to the Supreme Court yesterday in Commil v. Cisco, a patent case that asks whether having a “good-faith belief” that a patent is invalid means that someone can’t induce infringement of a patent.

The issue of what it means to “induce infringement” is a complex, esoteric area of patent law. Generally, inducement liability is where the person accused of infringement didn’t actually carry out infringing acts herself, but instead encouraged other people to do them. For example, telling someone “hey, use this product to infringe this patent” might be inducement, whereas just making a product without any knowledge of a patent on its use would not be.

That’s because the law requires that the inducer have knowledge of the patent in order to be liable. But what if you have knowledge of the patent and you think that it is invalid because it’s not clear what the invention is, or that you don’t infringe because you don’t think the patent covers what your customers do? A court may later determine that you were wrong, but agree with you that you had a reasonable belief that you were right. Should the law make you pay for encouraging something you reasonably thought you were allowed to do?

In our brief, we argue that inducement requires intent to infringe and if you think you’re not infringing (because either the patent is invalid or because you don’t think the acts you cause are covered by the patent), you shouldn’t be considered an inducer.

A contrary ruling would encourage patent holders to avoid clearly describing their inventions in a patent which would exacerbate the problem we already have with vague and overbroad software patents. Patent applicants could hide the ball from the Patent Office (making it more difficult and time consuming to do a good job reviewing the application) and the public (who may not understand the rights claimed by the patent holder), and still claim someone should have known that what they were doing was causing other people to infringe.

Patents serve a public notice function: they are supposed to reasonably inform the public of what is claimed and what is left free for others to do. But the rule the patent owner argues for in this case would make the public notice function of patents almost meaningless. For example, someone reading the patent may not think it applies to acts they cause, but because the court would only look to what the patent owner thinks (an opinion that doesn’t have to actually be stated in the patent), reading the patent may give no clue as to whether you’ll be accused of inducement. The Supreme Court should not allow patent owners to set even more traps for those who have no intention of infringing any valid patent.