Doctrine of equivalents
The doctrine of equivalents is a legal rule in most of the world's patent systems that allows a court to hold a party liable for patent infringement even though the infringing device or process does not fall within the literal scope of a patent claim, but nevertheless is equivalent to the claimed invention. U.S. judge Learned Hand has described its purpose as being "to temper unsparing logic and prevent an infringer from stealing the benefit of the invention".
The goal of the doctrine of equivalents is to provide patent owners with fair protection for their patents. Historically, courts took a literal approach to patent interpretation, based on established principles of legal interpretation. However, by the 18th and 19th centuries, this had come to be seen as unduly limiting on the scope of protection afforded a patent-holder, especially as patent applicants are often required to describe new technology for which an adequate vocabulary has not yet been developed. In response to this, the English courts developed a so-called 'pith and marrow' approach, which tried to distinguish between the essential and non-essential features of a patent claim when deciding infringement cases. At the same time, courts in other countries, notably the United States, developed slightly different approaches to claim interpretation, of which the 'doctrine of equivalents' is perhaps the most famous. The equivalents doctrine takes a more holistic approach when comparing the patented invention with an alleged infringing device than did the 'pith and marrow' approach.
Attempts are ongoing at harmonizing the different approaches internationally (see below); however, progress is slow due to the long history of patent law in developed nations. The doctrine has been criticized[by whom?] as unduly vague, to the extent that it injects uncertainty and unpredictability to a patent system.
Standards for determining equivalents
In Germany, a device is considered to be equivalent if there is identity between the device and the claimed invention with respect to the problem and the effect, but not necessarily the "solution principle" (the manner in which the device operates).
Ireland appears to subscribe to a doctrine of equivalents. In Farbwerke Hoechst v Intercontinental Pharmaceuticals (Eire) Ltd (1968), a case involving a patent of a chemical process, the High Court found that the defendant had infringed the plaintiff's patent despite the fact that the defendant had substituted the starting material specified in the patent claim for another material. Expert evidence showed that any technician who failed to obtain a good result using the specified starting material would try the replacement material. The two materials were therefore held to be chemically equivalent, and the replacement of one with the other by the defendant did not prevent a finding and injunction against him.
Japan's doctrine of equivalents was first formalized in 1998, when Japan's Supreme Court held that equivalents are determined by considering (1) whether the difference relates to an important claim element, (2) the possibility for substitution without causing a failure to attain an invention's object and a change in the manner of attaining it, (3) obviousness of the substitution, (4) whether the accused item is an anticipated or obvious modification of state of the art, and (5) whether estoppel exists.
The United Kingdom has never employed a doctrine of equivalents approach. This was most recently asserted by Lord Hoffmann in Kirin-Amgen Inc v Hoechst Marion Roussel Ltd (2004). As a signatory to the European Patent Convention (EPC), the UK follows the Protocol on the Interpretation of Article 69 of the EPC, which requires member states to draw a balance between interpreting patent claims with strict literalism (with the description and drawings only helping resolve ambiguity) and regarding the claims as a mere guideline only.
The latest UK case law on claim interpretation is found in 'Improver Corp v Remington Consumer Products Ltd' (1990) and the House of Lords decision in 'Kirin-Amgen' (2004). The so-called 'Improver' (or Protocol) questions found in the former are a widely used three-step test for deciding infringement. Their usefulness in high-tech cases was, however, called into doubt by Lord Walker in 'Kirin-Amgen'.
In the United States, the doctrine of equivalents analysis is applied to individual claim limitations, not to the invention as a whole. The legal test, articulated in Warner-Jenkinson Co. v. Hilton Davis Chem. Co. (1997), is whether the difference between the feature in the accused device and the limitation literally recited in the patent claim is "insubstantial."
One way of determining whether a difference is "insubstantial" or not is called the "triple identity" test. Under the triple-identity test, the difference between the feature in the accused device and the limitation literally recited in the patent claim may be found to be "insubstantial" if the feature in the accused device:
- Performs substantially the same function
- In substantially the same way
- To yield substantially the same result
as the limitation literally recited in the patent claim. See Graver Tank & Manufacturing Co. v. Linde Air Products Co., (1950).
The Court also explained that the doctrine of equivalents applies if two elements are interchangeable and a person with ordinary skill in the art would have known that the elements were interchangeable at the time of infringement. 
In the United States, the doctrine of equivalents is limited by prosecution history estoppel. Under prosecution history estoppel, if the patentee abandoned through an amendment to the patent application certain literal claim coverage (e.g., by narrowing the literal scope of the patent claim), then the patentee is estopped from later arguing that the surrendered coverage is insubstantially different from the literally claimed limitation. Other more arcane limitations such as the ensnarement defense tend to be more difficult to apply.
The United States also has a statutory equivalents doctrine that is codified in 35 U.S.C. § 112 ¶ 6, which extends to structural equivalents. However, while the doctrine of equivalents for ¶ 6 extends to technological equivalents developed after the issuance of a claim, the structural equivalents of ¶ 6 only extends to equivalents available at issuance and disclosed in the application.
Attempts have been made to harmonize the doctrine of equivalents.
- "(a) (...) a claim shall be considered to cover not only all the elements as expressed in the claim but also equivalents.
- (b) An element ("the equivalent element") shall generally be considered as being equivalent to an element as expressed in a claim if, at the time of any alleged infringement, either of the following conditions is fulfilled in regard to the invention as claimed:
- (i) the equivalent element performs substantially the same function in substantially the same way and produces substantially the same result as the element as expressed in the claim, or
- (ii) it is obvious to a person skilled in the art that the same result as that achieved by means of the element as expressed in the claim can be achieved by means of the equivalent element."
The EPC 2000, which came into effect on 13 December 2007, included an amended "Protocol on the interpretation of Article 69 EPC" intended to bring about uniformity at a national level between contracting states to the EPC when interpreting claims. The amended text reads:
- For the purpose of determining the extent of protection conferred by a European patent, due account shall be taken of any element which is an equivalent to an element specified in the claims.
However, no definition of what was meant by an "equivalent" was included in the Protocol and it is expected that this lack of a binding definition will do little to achieve the desired uniform interpretation.
- United States
- United Kingdom
- Royal Typewriter Co. v. Remington Rand, Inc., 168 F.2d 691, 692 (2d Cir. 1948).
- See Warner-Jenkinson Co.
- See Warner-Jenkinson Co.
- See Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.
-  Depuy Spine, Inc. v. Biedermann Motech GMBH (Fed. Cir. 2009)
-  Chiuminatta Concrete Concepts, Inc. v. Cardinal Industries, Inc. (Fed. Cir. 1997)
- "An Overview of the New European Patent Convention and its Potential Impact on European Patent Practice", S.J. Farmer and M. Grund, Bio-Science Law Review, Vol. 9, Issue 2, pages 53-61
- Meurer, Michael J. and Nard, Craig Allen, "Invention, Refinement and Patent Claim Scope: A New Perspective on the Doctrine of Equivalents" (April 20, 2004). Boston University School of Law Working Paper No. 04-03; Case Legal Studies Research Paper No. 04-5. 
- Rigamonti, Cyrill P., "Conflicting Theories of Equivalence: 35 U.S.C. § 112, para. 6 in the Federal Circuit and the Supreme Court", 40 IDEA: The Journal of Law and Technology 163 (2000), 
- "Patent Law: The Festo Case and the Doctrine of Equivalents", United States Congressional Research Service, July 25, 2002