The reverse doctrine of equivalents is a way for courts to find that an invention does not actually infringe on a patent, even if it appears to do so in a technical sense. While the doctrine of equivalents expands the scope of the patent infringement claims, the reverse doctrine of equivalents narrows their scope, so that a new invention might not infringe on a patent, even if it is substantially similar to an invention that has already been patented.

The reverse doctrine of equivalents is an affirmative defense to a claim of patent infringement. It might be used to avoid a finding of infringement, even if, technically, there is infringement in some technical respects. The doctrine comes from an 1898 U.S. Supreme Court case in which the Court prescribed two elements that must be present for a court to conclude that a patent has been infringed. They are as follows:

  • The patent holder must show that the object that allegedly infringes on the patent comes within the scope of the patent claim; and
  • The patent holder must show there is substantial identity between their patented invention and the invention that allegedly infringes on the patented invention.

The doctrine of equivalents comes into play with the first element of this test; there can be patent infringement even if the two items are not the same in every detail. There can be infringement if the differences between the two items are not substantial differences, and the two items are equivalent.

The reverse doctrine of equivalents plays a role with respect to the second element of this test. In 1898, the Court stated that an invention that comes within the literal definition of an infringement, because it is substantially the same, or equivalent, can avoid infringement if it performs the same function as the patented item, but in a substantially different way.

So, in other words, per the reverse doctrine of equivalents, a device that appears to infringe on a patented device, because it includes elements or limitations that correspond to each element or limitation of the patented device, does not infringe on the patent, because the device operates on a different principle.

That is, “it performs the same or a similar function in a substantially different way.” It has been said that “the purpose of the ‘reverse’ doctrine is to prevent unwarranted extension of the claims beyond a fair scope of the patentee’s invention.”

When Can I Use the Reverse Doctrine of Equivalents?

In a patent infringement case, the patent holder bears the burden of proving infringement by a preponderance of the evidence. The patent holder succeeds when they prove factual infringement on their patent. At that point in the proceedings, the person accused of infringing on the patent may elect to offer evidence of noninfringement under the reverse doctrine of equivalents.

If the person claimed to have infringed the patent makes a prima facie case, the patent holder, who still has the burden of persuasion on infringement, must produce evidence that refutes the case for noninfringement and bolsters the case on the side of infringement.

There is some confusion in the law regarding the reverse doctrine of equivalents and how it can be applied in a case of alleged patent infringement. In one case, the federal court stated that the accused infringer must establish the principle on which their object operates so as to prove that it is different from that of the patented object. The court held that supplying the opinion of one expert to the effect that an object operates on a different principle is not good enough to defeat a summary judgment motion brought by the patent holder.

Apparently, the reverse doctrine of equivalents is used only rarely in cases where the new invention has significantly changed in principle but still falls under the literal claims of the patented invention. The courts use the reverse doctrine of equivalents to avoid finding infringement, only if it would be very unfair or very detrimental to prevent the new inventor from making his invention.

Knowledgeable experts have expressed the opinion that greater use should be made of the reverse doctrine of equivalents, because it would serve an important public purpose. They note that a large number of patented inventions exist, but most of them are never brought to market in commercial form for the benefit of the public. They serve only to stifle innovation of equivalent products and keep them off the market.

The reverse doctrine of equivalents could be used by the courts to excuse alleged patent infringement when appropriate in a particular case. This would prevent the U.S. patent system from stifling technological innovation. It could be used in cases in which the product that allegedly infringes on a patented product represents a significant improvement on a patented invention.

How Does the Reverse Doctrine of Equivalents Work?

Federal courts have made comments that throw the usefulness of the reverse doctrine of equivalents into confusion. One federal Circuit Court of Appeals has claimed that there has never been a case in which a court found noninfringement on the basis of the reverse doctrine of equivalents.

In another case, a different federal Circuit Court wrote that “’the doctrine is rarely invoked and virtually never sustained,” meaning that it is used only very rarely and has never been successful. Because of statements such as these, some federal District Courts have questioned whether the reverse doctrine of equivalents is still even a viable doctrine in patent infringement cases.

One District Court has explicitly stated that the reverse doctrine of equivalents is “arguably moribund,” while another has written that it must be assumed to be available until a higher court explicitly holds that it is not.

In determining whether or not to apply the reverse doctrine of equivalents, a court will consider several factors:

  • The actual scope of the patent and whether it covers the new invention;
  • If it does, whether the patent should extend to the new invention. This is the major issue that the reverse doctrine of equivalents must address, i.e. what is the fair scope of the patent is and whether or not a new invention comes within it;
  • Whether the new invention has sufficiently transformed the original invention to the extent that it should fall outside the scope of the patent that applies to the original.

So, the question of how the reverse doctrine of equivalents works does not have a ready answer. It is complicated and could well depend on the particular federal court in which a suit for patent infringement is brought. It would also depend on the facts of a particular case.

Do I Need a Patent Lawyer?

To successfully bring a lawsuit for patent infringement you do need to consult an experienced patent lawyer. An patent lawyer has the expertise necessary to advise you on all aspects of patent law, from getting a patent to protecting patent rights from those who would want to infringe on it.

An intellectual property lawyer can also defend you if you have been sued for patent infringement. They can clarify whether the reverse doctrine of equivalents might help you in your case.