The inherent nature of Intellectual Property Rights (IPRs) is negative in nature since they enable the exclusion of unauthorized use over the subject matter that is new, useful, and non-obvious. This exclusion is attempted to be avoided by unauthorized users by inventing around the scope of the claims of the parent patents. However, over the past many years, the principle of equivalence is being deployed to ensure that the limitation of language does not create a loophole in the enjoyment of such rights in favor of the original proprietor of rights. In the absence of such a doctrine, such proprietary rights would lose their value and essence since it would open different routes of making infringement possible.

What is the Doctrine of Equivalence?

Speaking of Patent Infringement, it can either be literal or non-literal. ‘Literal Infringement’ would mean an exact cut, copy, and paste replica of the original patented invention. It was visible in the case of Polaroid Corp v. Eastman Kodak [1986], wherein Eastman Kodak directly used the Plaintiff’s ‘instant camera technology,’ which was considered to be a literal duplication of the said patented invention. On the other hand, non-literal infringement may be accidental or might be pursued in bad faith as well. To quote an instance of indirect infringement, in Ravi Kamal Bali v. Kala Tech and Others, the end-product varied in terms of appearance; however, it was similar in terms of functionality and construction. This is where the ‘Doctrine of Equivalence’ comes to play.

The Doctrine helps identify the core similarity underlying the two products placed in comparison with one another while they may actually not appear identical at a glance. Therefore, it enables the identification of similar claims, which may not be literally visible. Additionally, it prevents third-party users from benefiting from the invention made by another by simply making minuscule alterations while retaining the invention’s functionality.

Mapping the Historical Development of the Doctrine of Equivalence

The Doctrine was curated by the US Supreme Court, which can be traced way back to 1853 in Winans v. Denmead, wherein the Court acknowledged that patents would deem valueless if they could be exploited by introducing a slight change in the invention by molding the literal language. Therefore, the Court ruled that infringement may also occur in cases where the literal language of the claims is avoided.

In Graver Tank and Mfg Company v. Linde Air Prods Inc, the Doctrine developed better shape and meaning. The Court laid the triple test, wherein the Doctrine is said to be present when a substituted element is capable of substantially performing the same function in substantially the same manner to obtain the same result. While applying the said test, it is also crucial to ascertain the obviousness of the substituted segment as per the person who is skilled in the relevant art.

The Doctrine further developed in Warner-Jenkinson Co. v. Hilton Davis Chemical Company, wherein the Court laid the ‘all elements test.’ As per this test, the Doctrine of Equivalence shall be applied to each claim independently and not to the entire invention as a whole. Therefore, it is imperative to establish that all the elements of the patented invention could be found in the infringer’s invention.

Limitations to the Doctrine of Equivalence

Although the Doctrine provides a haven for patented inventions, there are still different limitations that prevent a patentee from taking this route to defend his invention. The limitations are as follows:

  1. Disclosure-Dedication Rule: This rule was established by the US Supreme Court in 1881, which states that when the claims of an invention suggest different alternatives or combinations that are not prima facie claimed by the said patent, then such unclaimed segments/alternatives are nothing but a dedication to the public. The patentee cannot rely on its claims by stating that since it is mentioned in the disclosure (application), it is simply claimed. The Doctrine of Equivalence would not come to the rescue of such patented inventions against which may seem potential infringers to capture the disclosed but unclaimed alternative. In a much recent judgment, the Federal Court in Eagle Pharms v. Hospiradecided that the patentee could not resort to the Doctrine of Equivalence only because it mentioned “a pharmaceutically acceptable fluid which contains one or more of propylene glycol, ethanol, polyethylene glycol, benzyl alcohol, and glycofurol” while it actually claimed propylene glycol.
  2. Ensnarement: The Doctrine of Equivalence cannot be deployed to seek the protection of those elements of a claim that are obvious or have been reflected in the prior art. In Gevo v. Butamax Advanced Biofuels,the Court held that where a patentee narrowed a claim to cover a single bacterial enzyme to avoid a rejection based on ‘obviousness,’ the patentee could not resort to the Doctrine of Equivalence because the hypothetical claim covering the alleged equivalent would have been obvious over the existent prior art.
  3. Prosecution History Estoppel: This is a significant limitation according to which a patentee is prevented from obtaining under the Doctrine of Equivalence elements of the subject matter that had been relinquished during the prosecution of the relevant Patent Application. In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., the US Supreme Court summarized the doctrine of prosecuting history estoppel as follows:


  1. Any narrowing amendment made to satisfy the requirements of the Patent Act may give rise to estoppel;
  2. An unexplained narrowing amendment is presumed to have been made to satisfy the requirements of the Patent Act;
  3. Estoppel does not create an absolute bar to the application of the Doctrine of Equivalents and can be rebutted by the patentee on account of the equivalent being new or unforeseeable when the amendment was actually made;
  4. The applicant is presumed to have surrendered the scope of protection between the claim before amendment and after amendment; and
  5. It is the applicant’s burden to show that the particular equivalent in question was not surrendered.

Underlying Problems within the Doctrine of Equivalence

As noted above, the limitation of language is a real shortcoming in assessing the genuineness of a patented invention as one simple meaning can be conveyed in several different ways. While the Doctrine of Equivalence may try to provide a solution to this problem, it certainly does not promote the public notice function.

If a random member from the public audience creates an invention (after reading and reviewing the patent) that falls outside the literal scope of the claims of the parent patent, which is later found to have infringed upon the same patent under the Doctrine of Equivalents, the notice function served by the claims simply fails. The same has been often observed when inventors try to design around an invention in good faith and are caught up under the accusation of infringement caused through the application of the Doctrine of Equivalence. The Doctrine may introduce fair dicta in favor of the parent patent’s inventor but certainly abridges the rights of others by imposing a high social cost, which may impede innovation in the long run.



While looking from the point of view of the potential infringer, the inventor may never be too sure whether the Court will interpret the facts of a case in his favor even though he may have tried to steer clear from all the literal claims of the parent invention in the face of application of the Doctrine. Similarly, the inventor may never be too sure whether to use the Doctrine in support of his arguments as the Doctrine is highly subjective and unpredictable in nature. Therefore, the Doctrine may not always bear fruitful or favorable results in the realm of non-literal infringements. Even though it may have its own drawbacks, the Doctrine cannot be ignored in the face of the threat of bad faith infringements.