Patent claims typically are the delimiting language that outlines the extent of the rights granted in a patent. These rights can continue unchanged throughout the term of a patent – typically 20 years for a utility patent. Most of the time, that’s what happens. However, there are circumstances where patent claims are not the last word as to patent infringement.
Patent law allows for “intervening rights,” or rights to would-be infringers of issued patents, under two very specific circumstances. These circumstances include those when the scope of a patent is changed by either reissue or reexamination. Fairness to the would-be infringer is the essence of intervening rights. If patent claims change in scope during the life of the patent, it is fair to allow unpunished infringing activities that might otherwise be patent infringements because the would-be infringers would have had no way of predicting the final scope of the patent claims. In other words, the world is only on notice once – at the time the patent issues – for avoiding activities that may infringe the claims. Intervening rights are provided by statute and by equity.
REISSUE. In the reissue statute, 35 U.S.C. 252, two types of intervening rights are established. In a reissue, the patent owner asks the patent office to allow for additional claiming of subject matter that while supported in the original disclosure, was defectively claimed, or inadvertently not claimed. As a result, new claims, granting new and broader scope, may be added to the patent. To protect those who have relied, in good faith, on the original grant of the patent to delineate the bounds of its claims, absolute intervening rights are granted to those who, “prior to the grant of a reissue, made, purchased, offered to sell, or used unless such thing infringes a valid claim of the reissued patent which was in the original patent.” Such intervening rights are mandatory upon the court.
A second class of intervening rights, equitable intervening rights, is extended even to those who made “substantial preparation” to practice an aspect of the invention later barred by a new claim in the reissue. These equitable intervening rights are within the discretion of the court.
The difference between absolute and equitable rights can be important in an infringement defense. Equitable rights, the weaker of the two intervening rights, are an affirmative defense and are waived if not pleaded, or at least raised, at trial during the liability phase of the lawsuit. Contrarily, failure to raise the issue of absolute intervening rights is not a waiver of those rights; these rights can be raised even after the liability phase of a patent lawsuit has concluded.
REEXAMINATION. 35 U.S.C. S 307(b) provides for intervening rights following reexamination. A reexamination re-opens a patent to new scrutiny by the patent office, and existing claims may be lost, or new claims approved. If a claim is amended, or a new claim allowed, the effect is similar to that of a reissue patent. Absolute rights are granted to those actually practicing an activity infringing a new claim, while equitable rights are granted to those who may have made “substantial preparations” to do so.