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Delhi High Court: In a dispute relating to patents, it is important to assess the pith and marrow of the invention

In a recent case before the Delhi High Court, the court discussed the “Doctrine of Equivalents” and how the pith and marrow test ought to be used alongside the triple identity test for establishing a possible infringement.

Background of the case:

The plaintiffs claimed to be a pioneer in revolutionizing brickmaking process and had plurality of patents on fully automated and mobile brick making machine (“plaintiffs’ machines”). 

The plaintiffs alleged that defendant was infringing their patent by manufacturing and selling Brick Making Machines (“defendant’s machine”) which had all the essential elements of the Plaintiffs’ machines. 

The Plaintiffs had issued a Cease-and-Desist Notice to the Defendants, to which the defendants did not respond.

The Plaintiffs then filed the present suit and inter alia sought permanent injunction restraining the defendants from making, manufacturing, selling the impugned machines without the license of the plaintiffs.  The plaintiffs also sought relief relating to infringement of copyright regarding specification/ artistic features related to the literature of the impugned machine.

Submissions of the Parties: 

The Plaintiffs submitted that as the differences in the Plaintiffs machine and the Defendants machine were insignificant and trifling. The present case was not a case of literal infringement where each and every component was copied but the substance of the invention was copied. 

The plaintiffs applied the ‘Doctrine of Equivalents’ and reiterated that a simple comparison showed that plaintiffs’ and defendant’s machine were achieving the same result through a similar integration causing infringement of the Plaintiffs rights.

The balance of convenience was in favour of the Plaintiff’s, and they had invested for the research and development of the machine. Irreparable loss and injury would be caused if the injunction was not granted. 

The Defendants’ averred that automated brick making machines should be regarded as ‘prior art’ as brick making machines were already available. It was the case of the Defendants that the plaintiffs had failed to establish a prima facie case of infringement.  

According to the Defendants, the ‘Doctrine of Equivalents’ was not applicable as the doctrine, when applied to mechanical devices requires satisfaction the triple test i.e. Function-Way-result [FWR] test. 

The Defendants submitted that ‘all elements rule’ would apply which was the traditional test across jurisdictions. 

The defendants also argued that the defendant was making a static machine, but the farmer was making it mobile by using his tractor. 

During rejoinder the Plaintiffs inter alia reiterated the pith and marrow of the patent had to be seen for the purposes of patent infringement and the doctrine of equivalents was applicable. 

The Courts analysis and Order: 

The Court mapped the differences between the machines of the plaintiffs and the defendant through the designs and the pictures submitted by the parties.

The court observed that very often infringers deploy minor variations in a product which employs multifarious elements and argue that it does not infringe, even though it performs the same function in substantially the same way to obtain the same result. The essence of the ‘Doctrine of Equivalents’ is that an infringer should not be able to get away with a fraud on the patent by merely arguing that some elements of the plaintiff's products are not present in that of the defendant. 

The court opined that in patents jurisprudence, the essential idea of applying for a patent and being granted the same is for the commercial exploitation of the patent. If a patentee’s product is ambushed by an infringer’s product albeit with minor variation(s), it defeats the very purpose of the patent. Usually, the primary objective and mission of the infringer is to produce a product which competes with product of the plaintiff in the market and therefore, the FWR or the triple identity test becomes critical. It is crucial that the pith and marrow test ought to be used alongside the triple identity test in establishing a possible infringement. The all-elements rule cannot be adopted to the exclusion of the pith and marrow rule. 

In the present case, at first blush, it would seem that the differences would secure the defendant from an infringement action; however, if one looks closely at the differences cited, all the differences cited are really parts of the same fundamental issue, i.e., the mobility and the mechanism to ensure mobility of the assembly. The pith and marrow of the invention is really the assembly which ensures brick making through mobility. 

It is not the defendant’s case that their brick making machine did not require mobility at all. In fact, without mobility defendant’s machine would serve no purpose considering it had a roller and die mechanism as well. Therefore, the assertion that there were fundamental changes in the defendant’s machine were not correct and difficult to countenance. 

The Court granted the interim injunction to the plaintiffs and held that the plaintiffs have made out a prima facie case of infringement and the balance of convenience also lies in their favour. Irreparable injury would be caused if the injunction is not granted. 

A brief glance on the doctrines and rules discussed in the case

Doctrine of Equivalents: 

The doctrine states that if a product has minor differences, with the intention to avoid “literal” infringement, it will still amount to an infringement if the products do the same work and yield similar results even though they may differ in shape, size or form. 

The all-elements rule and the triple identity test of function, way, and result, [FWR] are two tests that are applied to test the applicability of the doctrine. 

All elements rule: 

All element rule states that every part of a claim must be present in a device that is accused of infringing the patent in order for it to be considered a literal infringement. This rule is used to limit the application of the doctrine of equivalents and ensure that it only applies to individual elements of a claim rather than the entire claim.

 It is also to ensure that patent owners are only able to enforce their patents against devices that truly infringe on their claims, rather than devices that may have some similarities but do not meet all of the claim elements. 


The “Function-Way-Result (FWR) Test” is a three step determination 

1. The “Function” test to checks if the device performs substantially the same function as the patent;

2. The “Way” test to check if the device works in a substantially similar manner as the patent and

3. The “Result” test to evaluate if the device produces similar result as the patent.

Doctrine of pith and marrow:

The pith and marrow doctrine, also known as the substance of the invention doctrine requires the courts to look beyond the literal wording of a patent claim and instead focus on what the invention actually does. It involves a careful analysis of essential features of the patent claim for comparison with the allegedly infringing product or process. 


The order has upheld the doctrine of pith and marrow and borrowed the “all elements rule” from the ‘Doctrine of Equivalents’ to arrive at the present order. However, one must be cautious while interpreting the judgement and ensure that it does not lead to a monopoly of the patent holder over any other device which would produce the same result.  

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