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".
Standards for determining equivalents
German courts typically apply a three-step test known as Schneidmesser's questions. These questions are:
- Does the variant solve the problem underlying the invention with means that objectively have the same effect?
- Would the person skilled in the art, using the common general knowledge, have realised at the priority date that the variant has the same effect?
- Are the considerations which the skilled person takes into account for the variant in the light of the meaning of the invention close enough to the considerations taken into account for the literal solution protected by the claims, such that the skilled person will consider the variant as a solution which is equivalent to the literal one?
All of the above questions need to be answered in the affirmative in order to demonstrate equivalent infringement. In addition, an allegation of equivalent infringement needs to withstand the Formstein test. The corresponding question reads:
- Does the variant, having regard to the state of the art, lack novelty or is the variant obvious to a person skilled in the art?
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.
- Does the substitute satisfy to the same objective function (same effect)?
- Based on the patent, are the substituted features and their same objective function made obvious to the skilled person in the art (accessibility)?
- Would the person skilled in the art nevertheless have considered, based on the language of the claim, that the substituted features are a solution of the same value (same value)?
The court denied equivalent infringement since the answer to the third question was negative.
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. The proposed equivalents also cannot cover, or ensnare, the prior art.
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).
- Schneidmesser II; GRUR 2002, p 513. Federal Court of Justice of Germany, March 12, 2002.
- Schneidmesser II; GRUR 1986, p 803. Federal Court of Justice of Germany, April 29, 1986.
- Kontrazeptiva; GRUR Int 2014, p 543. Federal Patent Court of Switzerland, March 21, 2013.
- 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) (PDF, 1.5 MB)
- "Patent Law: The Festo Case and the Doctrine of Equivalents", United States Congressional Research Service, July 25, 2002