This article has been written by Namrata Kandankov, pursuing the Diploma in Intellectual Property, Media and Entertainment Laws from LawSikho.

What does the doctrine of equivalents entail? 

The equivalent doctrine is a legal mechanism that enables the inventor to file an infringement claim for his patent. Such a claim can rightfully be made by the inventor even though the original product is not the exact same as the infringed product. Protection can be granted to inventions through the “Doctrine of equivalents.” The doctrine of equivalence instills fear in the minds of people. It stops them from making even minor changes to the already patented inventions. The inception of the doctrine of equivalents dates back to Graver Tank and Manufacture Co. v. Linde Air Prods., Inc. The court’s ruling, in this case, gave birth to the triple identity test. This test shall be discussed in detail in the latter segment of the article. 

The standards to determine the equivalents in the doctrine of equivalent 

There have been a number of tests prescribed to determine the equivalents in the Doctrine of Equivalents (DOE). These rules, claims, and tests have been discussed below:

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1. The hypothetical claim

One of the ways in which a court determines the equivalents is through the hypothetical claim. The hypothetical claim is used to determine if there has been an infringement on an existing patent. The hypothetical claim particularly refers to infringement through the copying of prior art of the patented invention. The prior art of the original invention is copied in such a way that the consumer assumes the copied product serves the same purpose as that of the original one. An example of such a prior art being copied can be seen in the following case- Intendis GMBH v. Glenmark Pharmaceuticals Inc., USA.

A. Brief facts

 A gel was manufactured by Bayer. It treated a skin condition. Bayer was associated with the GMBH company. The gel was a registered patent under‘070 patent. Glenmark on the other hand made a generic gel. It further claimed the patent did not apply. The contention by Glenmark was based on the datum that generic gel contained various inactive ingredients. Another important aspect that was in question was the lecithin content. Glenmark stated that there was no lecithin in the generic gel. However, Glenmark could not prove the same. Hence, it was concluded by the court that Glenmark had the same ingredients as Bayer’s. 

B. Application of DOE in the case

The court, in this case, arrived at a conclusion that DOE applies even if the patent does not spell out the functions. This is because the gel manufactured by Bayer’s performed the same functions as that of Glenmark. Further, the ingredients of both the gel were not considerably different. Hence, the court ruled that DOE applies even if the patent does not spell out the results, way, and functions. It was concluded from this case that making minor changes to the product does not invalidate its patent. Hence, DOE rightfully applies even if a product is limited in its description. 

Limitation of the DOE 

Generally speaking, there are three major limitations to the DOE. They are:

  1. The patent holders are limited by the claim that exists in their patent. 
  2. The difference between the two inventions ought to be minor. 
  3. Equivalents can’t be used to encompass the prior art. 

The hypothetical claims usually address the third limitation. The hypothetical claim examines if an equivalent claimed by the inventor would have been granted in their original patent. If the same cannot be granted, it cannot be used in a DOE case. Three major purposes have been served through this. They are:

  • The inventions in the public domain are protected.
  • The powers of the Patent and Trademark Office are reserved in terms of governing the prior art. 
  • Lastly, the defendants are prevented from the undue burden. 

2. The “All Elements” test 

The All Elements test categorically states that the DOE ought to be applied to all the individual elements of the claim and not the claimed invention as a whole. This test states that it is important to prove that every single element of the patented invention is present in the product of the accused. Such elements present in the product of the accused person should be substantial equivalents of the original product. This indicates that these elements should meet the requirements of the triple identity test. Further, equivalency should be considered only when a claim has been filed. The same should not be invoked when the product has been patented. 

3. The triple identity test contends the following

If two devices accomplish the same task elementarily in the same manner and attain the same output, then they are considered to be the same even when there are variations in shape, size, and form. There are a number of factors related to sustainability. They have been discussed below:

  1. If it was possible for a skilled person in the art to have known such an equivalence. 
  2. Whether an accused person intended to copy or did he just intend to design around and unintentionally arrived at the same results.
  3. If the persons skilled at the art actually know about the existence of the equivalence of the claimed and the accused inventions. 

Another significant aspect should be taken note of here. In the event there is equivalence between the process or the elements of the accused product and the claimed elements of the patented invention, it would amount to infringement. This shall hold good even when there is no infringement on the express terms of the patented claim. 

4. The amending claims

A patent can be issued for a claim different from the one it was filed for. Patents can also be rejected numerous times. The claims for registration should be such that it both provides descriptive information and is narrower. 

  • For Instance- Let’s consider an application being made to obtain a patent. And it gets rejected because of the prior art. Now the applicant in order to adjust the same, cannot make a claim broader than that of the prior art. The broader claims should be given up so that narrower claims can be approved. Hence, it means that the broader claims cannot be considered equivalent to the narrower claims. 

Further, the US Patent and Trademark Office (PTO) and most of the patent offices around the world maintain a list of rejected patents. This history of amended and rejected patents is usually stored in a paper jacket called ‘File Wrapper.’ Due to this, a claim is rejected, and then the refilling happens after the claim is narrowed down. 

Need for Doctrine of Equivalents 

A patent in the general notion includes the following:

  1. A specification,
  2. One or more claims,
  3. Drawings of the invention. 

When it comes to the infringement of patents, the important thing which matters is the claim. In order to determine infringement, each and every claim is read and compared to the actual invention. In most cases, the infringement is quite clear. However, in some cases, it is not. In certain circumstances, an inventor might include differences into their invention to get away with infringement. Such small differences can make differences unclear. Hence, there is a fire requirement of DOE. 

The DOE compares the inventions in adequate detail. The DOE appropriately examines how an invention works. It does not focus only on how the invention looks but goes beyond that. This subsequently allows the court to see superficial changes if there is an infringement present. 

  • The Vitiation rule- The vitiation rule is considered to be a common defense to the DOE rule. The vitiation rule comes into the picture when the DOE is used to make a claim term meaningless. In the event the jury could not find any two elements to be equivalent, the vitiation rule applies. The primary idea set forth by the vitiation rule is- as long as two elements function the same way, it does not matter if they have been designed differently. For the vitiation rule to apply, the elements being examined should be so different that there is no equivalency to be established. 


The DOE has been in existence for the past 150 years. However, there is still a need to jot down a legislative framework for the same. The absence of a legislative framework has created difficulty and ambiguity in terms of application. Speaking about the Indian scenario, very few cases of patent infringement on DOE have come to light. However, with the pace at which the technology is growing the judiciary is likely to face more and more cases in the coming year. Hence, there is a need to come up with a legislative framework for the same in both the Indian and the international scenarios.


  • Mary Green, The Doctrine and Equivalents and everything we need to know about it, Up Counsel, (published on 12th July 2018). 
  • Singh and Associates, Patent infringement and the Doctrine of Equivalents, Mondaq, (published on 30 March 2020).  
  • Preetesh Aggarwal, Understanding the Doctrine of Equivalent patents, iPleaders, (published on 7th October 2020). 

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