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.
The goal of the doctrine of equivalents is to provide patent owners with fair protection for their patents. As stated by the British House of Lords, "Copying an invention by taking its 'pith and marrow' without textual infringement of the patent is an old and familiar abuse which the law has never been powerless to prevent." (Per James, L.J., in Clark v. Adie (1873) L.R. 10 Ch. 667). However, the doctrine has been criticized as unduly vague, to the extent that it injects uncertainty and unpredictability to a patent system.
Standards for determining equivalents
In the United States, there are two tests for determining whether an accused device or process is deemed to be equivalent. Under the first test, called the "triple identity" test, something is deemed equivalent if:
- It performs substantially the same function
- in substantially the same way
- to yield substantially the same result.
Under the second test, something is deemed equivalent if there only an "insubstantial change" between each of the features of the accused device or process and the patent claim. One limitation that has been placed on this doctrine is prosecution history estoppel, which prevents a claim from being made for infringement where the difference is something that the patentee had abandoned through an amendment to the patent.
In United Kingdom, the doctrine of equivalents is defined as follows: an alteration of a claimed invention does not infringe the claim unless:
- it would have no material effect on the way the invention works,
- the lack of material effect would have been obvious to one skilled in the art at the date of publication, and
- it would be apparent to one skilled in the art that the patentee could not have intended the claim language to exclude such a known, minor variant having no material effect.
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).
Japan's doctrine of equivalents was first formalized in 1998, when Japan's Supreme Court held that equivalents are determined by considering (1) the possibility for substitution, and (2) the obviousness of the substitution.
In France, the doctrine of equivalents can be invoked if the accused device contains means having the same function in order to obtain the same result as the claimed invention.
Attempt were made in the past to harmonize the doctrine of equivalents.
For instance, Article 21(2) of 1991 WIPO's "Basic Proposal" for a Treaty Supplementing the Paris Convention states:
"(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."
On a strict European level, explicit introduction in codified law is planned as it can be seen in the new version of the European Patent Convention, the "EPC 2000". The new protocol on the interpretation of Article 69 EPC states, in its new Article 2:
"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."
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