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This article is written by ADITI TIWARI , BA LLB during her internship with Le Droit India.


 This article will deal with the Doctrine of Equivalents in Patent Law. In this article it is discussed about what is the Doctrine of Equivalents , how it evolved, its application and its applicability in the Indian context.


Doctrine of equivalents

Patent law


Under the doctrine of equivalents, a patent holder may assert an infringement claim even in cases where the allegedly infringing product does not contain every single element of the patented invention. The doctrine’s goal is to stop someone from using a patented invention without permission by making small, unimportant changes to it without affecting its functionality. If the accused product or process contains elements that are identical to or equivalent to each claimed element of the patented invention, that is the crucial question to answer when determining equivalency. An infringement action gives rise to the doctrine of equivalents. Under the doctrine of equivalents, an accused product or process may be found to be infringing even if it does not directly copy a patented invention.

Evolution of the Doctrine of Equivalents through Case Law

We will try to understand evolution of doctrine of equivalents through a case Winans v. Denmead. [1] The majority of authorities hold that the Winans v. Denmead ruling from the United States Supreme Court in 1853 served as the foundation for the doctrine of equivalents. When Winans was a child, railway ‘burden rail cars’, or vehicles meant to move bulky goods like coal or grain, were almost always made of straightforward rectangular boxes fixed to a rail car frame, either with or without a roof. Different pressure levels were applied to the rail car’s sidewalls by the weight of the material being transported; the highest pressure was found at the bottom of the sidewalls and the lowest at the top. This frequently resulted in the sidewall failing and the material being hauled spilling (or possibly being lost entirely). In terms of lost material and damage to the rail car, these kinds of failures were costly for the railway companies.

Winans changed the shape of the product’s container as a solution to this issue. The frustum, or the largest diameter part of a cone without the smaller diameter top, was the shape of Winans’ new container. Below, a frustum is displayed.

A figure illustrating the application of the new container shape is presented in the Winans patent . A gate or hatch cover was positioned at the bottom to facilitate the easy dumping of materials within the inverted conical frustum, which was fixed to the rail car frame.

Winans lowered the load’s centre of gravity and increased the car’s overall stability by positioning the container so that it extended below the rail car frame. According to Winans’ patent, his container shape allowed for almost twice as much material to be carried than conventional rectangular box-shaped rail cars by evenly distributing the load’s pressure on the sidewall from top to bottom.

When Winans learned that Denmead and associates were producing and marketing an octagonal (8-sided) container rail car with its 8 sides arranged in a conical circular pattern, he filed a lawsuit against them. The following illustrates the Denmead container’s basic configuration:

The judge decided during the trial that there was no patent infringement even though the patent was only intended for conical bodies and not rectilinear ones, given that the defendants’ car was fully rectilinear. The US Supreme Court heard an appeal from Winans. The Supreme Court overturned the trial court’s ruling in a significant decision pertaining to patent law, thereby establishing the foundational framework for the doctrine of equivalents. In a 5-4 ruling, Justice Curtis wrote on behalf of the Court, The patentee, having described his invention, shown its principles, and claimed it in that form which most perfectly embodies it, is, in contemplation of law, deemed to claim every form in which his invention may be copied, unless he manifests an intention to disclaim some of those forms.  This is the original doctrine.

The same functional advantages over conventional rail car design as claimed in the patent were demonstrated in the trial court testimony by Denmead’s octagonal design. These advantages included increased capacity, equal distribution of the load’s pressure across the container’s sides from top to bottom, and a lowered centre of gravity. Put differently, Winans’ patent gave Denmead’s octagonal design every advantage over previous art. The Court also pointed out that it is practically impossible to create a perfect circle and posed a rhetorical question regarding the degree of proximity required for an alleged infringer to be found in violation of the claim. The Court overturned the lower court’s ruling, holding that the jury should have been given the opportunity to decide the matter.

Applicability of doctrine of equivalent under patent law in Indian context 

As time goes on, new technology emerges every day, which has led to an increase in patent disputes more than ever before. The process of interpreting the language in a patent claim, or “claim construction,” to ascertain its scope and extent of coverage, is one of the most important aspects of patent disputes. The first crucial step in determining whether an accused infringer has violated the claim is claim construction or claim interpretation. Generally speaking, the language used in the claims must be interpreted objectively from the viewpoint of a person skilled in that specific art. The written description of the invention and the accompanying drawings, known as the patent specification, serve only as a backup source when it comes to interpreting a term or terms used in the claims where the meaning cannot be determined with certainty from other sources. The precise feature of the claims, however, might not always be present in the purportedly infringing process or product. Stated differently, it might not happen often for there to be a literal infringement of the claims.

On the other hand, taking the claims made against the alleged infringement literally could make it easier for the infringer to get around the advantages that would otherwise go to the original inventor and the legitimate owner of the patent. The courts may and have developed mechanisms whereby the rights of the inventor may be protected even in cases where the literal wording of the claim is not violated, in order to prevent such a farce from befalling the patentee. The Doctrine of Equivalents is one such tool, and the goal of this article is to examine and navigate the body of jurisprudence surrounding its application in India. Patent infringement occurs when a patentee’s exclusive rights are violated without their consent. When the patentee is able to prove that the infringing product or process, as the case may be, maps to every element in the patent claim and is commercially marketed without the patentee’s consent, then the most obvious line of attack against an alleged infringer is a literal infringement. However, the infringement may need to be examined more closely by, among other things, using the Doctrine of Equivalents when the infringer makes small, non-essential modifications to avoid violating the claim’s literal wording.

The Doctrine of Equivalents, which has developed from several US judicial precedents, basically allows the claim scope to be expanded to a certain extent while maintaining equity. The Doctrine as it currently exists is used to assess whether two devices—the one being claimed and the other being accused of infringement—achieve the same goal and function essentially in the same way. If they do, then they may be the same device even though they have different names, forms, or shapes. Therefore, the Doctrine of Equivalents may be applied to establish infringement even in cases where the allegedly infringing product or process deviates from the claims’ literal language as long as it fulfils the same function and achieves the same outcome as the claimed product or process. When determining whether the differences are substantial, the following considerations should be made:

1. If an individual with artistic talent would genuinely be aware that the two inventions under consideration are equivalent.
2. If an individual proficient in the arts would have been aware that the two inventions under consideration are equivalent.
3. Whether the purported infringer planned to mimic the invention or circumvent it to achieve the same outcome.

Indian courts have tried numerous times to acknowledge and implement the Doctrine of Equivalency in India, imitating US court rulings. An understanding of the development of the nature and extent of the applicability of the Doctrine of Equivalents in India can be gained from the discussion of several Indian judgements that follows.

The Court rejected the applicability of the Doctrine of Equivalents in Ravi Kamal Bali v. Kala Tech & Ors. (2008) 38 PTC 435, decided on June 3, 2008, and instead departed from the doctrine of pith and marrow as applied in Raj Prakash v. Mangat Ram Chowdhry & Ors[2]. In this case, Ravi Kamal Bali, the plaintiff, requested an injunction to prevent the defendants from violating his patent for a tamper-proof seal used on locking containers that he sells under the trade name “TECH LOCK.” The Plaintiff contended that the Defendant’s product performed the same function in essentially the same way and achieved substantially the same result, constituting an infringement of his patent, and that the differences between his invention and the alleged infringing product were superficial, cosmetic, and minor, meaning they were of no consequence. The Plaintiff argued that rather than requiring the infringing goods to be identical to the patented goods in every way, the court should apply the Doctrine of Equivalents when evaluating whether or not a device or process infringes a patent if it accomplishes the same function in a substantially the same way to produce the same result.

Defendants argued that their device did not substantially perform the same function as the Plaintiff’s device, even though it accomplished the same task to produce the same outcome. The evaluation was based on the steel spring that was one of the component’s materials. The Bombay High Court’s Singe Judge ruled that the defendant’s material was used for the same purposes as the plaintiff, that it was essentially the same material, and that a slight variation in the steel’s quality did not distinguish the material from the patented invention. The Plaintiff argued that the two products operated on the same principle and that any differences that were merely surface-level or cosmetic would not affect the invention as a whole, and the Court accepted this argument. It was determined that the Defendant had violated the Plaintiff’s patent due to the product’s identical functional and constructional features to the patented invention.

From the foregoing, it can be inferred that the court has occasionally acknowledged the Doctrine of Equivalents when reaching decisions regarding patent infringement cases.


Patent owners now have an additional avenue to safeguard their intellectual property when it comes to International Trade Commission exclusion procedures or Federal Court patent infringement cases thanks to the Doctrine of Equivalents. Our attorneys can assist you whether you are the owner of a patent or someone who has been accused of infringement by looking into whether patent rights are being violated directly or through the application of the doctrine of equivalents.

[1]  56 U.S. 15 How. 330 330 (1853)

[2] (2008) 38 PTC 435

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