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The Doctrine of Equivalents in Patent Law – An overview of the Law in India.

The Doctrine of Equivalents in Patent Law – An overview of the Law in India.


Determining patent infringement is a two-step process. First, the claims must be properly construed to determine their scope and meaning. Second, the claims, as properly construed, must be compared to the accused device.[i]

Literal infringement may be found if an accused device or method falls entirely within the scope of the asserted claims once properly construed, but there is no literal infringement if any claim limitation is absent from the accused device or method. [ii]

When literal infringement does not exist, infringement, in certain limited circumstances, may nevertheless be found under a judicially created doctrine called the “doctrine of equivalents.” [iii]

Under the doctrine, a product or process that does not literally infringe upon the express terms of a patent claim may nonetheless be found to infringe if there is ‘equivalence’ between the elements of the accused product or process and the claimed elements of the patented invention. [iv]

Emergence in the United States.

In discussing the foundational principles for what later became known as the doctrine of equivalents, the Supreme Court of United States (SCOTUS) in Winans v. Denmead [v] explained that the law required a patentee’s rights to extend beyond the literal form of the described invention, but to include all forms to which an infringer could copy the invention, i.e., a patent extends beyond its literal scope to include equivalents of the claimed invention. [vi]

The theory on which the doctrine is founded – the SCOTUS explained in Graver Tank & Mfg. Co. v. Linde Air Products Co [vii] – is that ‘if two devices do the same work in substantially the same way, and accomplish substantially the same result, they are the same, even though they differ in name, form or shape.’ [viii]

Graver Tank further illuminates on the subject – that in determining equivalents,  ‘consideration must be given to the purpose for which an ingredient is used in a patent, the qualities it has when combined with the other ingredients, and the function which it is intended to perform. An important factor is whether persons reasonably skilled in the art would have known of the interchangeability of an ingredient not contained in the patent with one that was.’ [ix]

In a case where an invention is expressed as a combination of elements, the SCOTUS in Warner-Jenkinson Co, Inc v Hilton Davis [x] observed that – ‘each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole’. [xi]

The Law in India.

The doctrine of equivalents has been accepted in the jurisprudence to protect patent rights from being infringed by infringers using colourable method of making some minor, insubstantial variations to escape the reach of the patent. [xii]

The doctrine is applied to ascertain whether there is an infringement by excluding any insubstantial, minor, or trivial changes that are designed to deprive the patentee of the benefits of his invention. [xiii] The doctrine is applicable only in cases where the variation or difference between the product or process and the patented claim is insignificant, insubstantial, and not essential to the patented claim. [xiv]

The law in India requires that to establish patent infringement, it is imperative for the court to reach a finding that ‘all the essential elements of the suit patents claimed’ are present in the patents being asserted. [xv] In other words, there is no infringement if an essential element is different or omitted. [xvi] There may still be infringement, however, if non-essential elements are substituted or omitted. [xvii]

The identification of elements as essential or non-essential is made: “(i) on the basis of the common knowledge of the worker skilled in the art to which the patent relates; (ii) as of the date the patent is published; (iii) having regard to whether or not it was obvious to the skilled reader at the time the patent was published that a variant of a particular element would not make a difference to the way in which the invention works; or (iv) according to the intent of the inventor, expressed or inferred from the claims, that a particular element is essential irrespective of its practical effect; (v) without, however, resort to extrinsic evidence of the inventor’s intention.” [xviii]

The doctrine of equivalents is applicable where a product or process is not identical to the claim granted in a patent but its essential elements are sufficiently similar to the patented claim, so as to construe the product or process as infringing the patent. [xix] A device which substantially performs the same function, in substantially the same way, and accomplishes the same result, may infringe the patent rights. [xx] The triple test – substantially the same function, in substantially the same way and to yield the same result – is applied primarily to products or devices. [xxi] Whereas for process patents, the essential elements of the given process; the necessary steps of that process; and the manner in which the essential elements interact at each step must be substantially similar to the patented process or method to sustain a claim of infringement. [xxii]


A suit for patent infringement must necessarily involve an exercise in claim construction to be undertaken by the court to determine the scope of protection of the Suit Patent. The doctrine of purposive construction is effected by the Indian Courts to assist in claim construction, which then could determine and distinguish between the essential elements and the non-essential elements of the claim being asserted. Once a determination of the essential elements is made, mapping can be undertaken with the infringing product / process where – if all the essential elements are found to be in the alleged to be infringing product / process, infringement is established and that is the end of the matter. Whereas the doctrine of equivalents could be pressed into service in order to determine the question of infringement if the differences as determined are of a non-essential nature. The court could in such cases, compare the elements to determine whether equivalency is to be found between the elements, in order to determine, if a case for infringement is made out.

[i] Lantech, Inc. v. Keip Mach. Co., 32 F.3d 542, 546, 31 U.S.P.Q.2d 1666, 1669 (Fed. Cir. 1994).

[ii] Amgen Inc. v. F. Hoffman-La Roche Ltd, 580 F.3d 1340, 1374, 92 U.S.P.Q.2d 1289 (Fed. Cir. 2009).

[iii] See ‘§ 13:1. Introduction to the doctrine of equivalents, 2 Annotated Patent Digest § 13:1’ by Robert A. Matthews, Jr. at p. 1.

[iv] Id.

[v] Winans v. Denmead, 56 U.S. 330, 342, 15 How. 330, 14 L. Ed. 717, 1853 WL 7544 (1853).

[vi] See ‘§ 13:1. Introduction to the doctrine of equivalents, 2 Annotated Patent Digest § 13:1’ by Robert A. Matthews, Jr. at p. 3.

[vii] Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605 (1950)

[viii] Id., p. 608.

[ix] Id., p. 609.

[x] Warner-Jenkinson Co, Inc v Hilton Davis Chemical Co., 520 US 17 (1997, Supreme Ct).

[xi] Id., p. 29-30.

[xii] FMC Corporation & Ors. v Natco Pharma Limited 2022/DHC/005311, at para 31, p.26.

[xiii] Id.

[xiv] Id.

[xv] See Sotefin SA v Indraprastha Cancer Society and Research Center & Ors. 2022/DHC/595, at para 28, p.27-28; FMC Corporation & Ors. v Natco Pharma Limited 2022/DHC/3749, at para 18, p.27-28; FMC Corporation & Ors. v Insecticides India Limited 2022/DHC/004770, at para 15, p.27-28.


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