The Doctrine of Equivalents in Various Patent Regimes: Does Anybody Have it Right?

Intellectual Property and Patents

Article Snapshot


Martin Adelman, Shamnad Basheer, Raj S. Davé, Peter Meier-Beck, Yukio Nagasawa, Nicholas Pumfrey, Martin Sulsky and Maximilian von Rospatt


Yale Journal of Law & Technology, Vol. 11, p. 261-308, 2009


This article analyzes and compares patent law’s doctrine of equivalents across four different jurisdictions.

Policy Relevance

The doctrine of equivalents, providing the scope of patent coverage, is one of the most important and difficult problems of patent law. The disparity between different legal solutions to this problem highlights the potential areas of reform as well as allows analysis of the costs and benefits of each system.

Main Points

  • Patent law allows for the inventor of a product or process to have exclusive rights for a finite period of time. This protection acts to incentivize invention and disclosure while also rewarding inventors for their work.
  • One of the most difficult areas of patent protection to define and regulate is the scope of a patent, which includes what has come to be called the doctrine of equivalents. This doctrine of equivalents prevents infringers and competing users from altering the disclosed product or process in some minor way while still preserving the use and function of the invention.
  • Most patent systems use some form of the doctrine of equivalents in order to maintain the integrity of the patent system. However, different systems have come to different methods for enforcing this doctrine.
    • The United States has left the doctrine of equivalents to the courts, which have enforced strong equivalency principles and often consider the patent prosecution history for the invention involved.
    • The United Kingdom uses the doctrine of purposive construction to solve the issue of patent equivalency. This approach attempts to determine the purpose behind the language of a patent claim and then determines if the potentially infringing claim falls within the bounds of the old claim’s purpose.
    • Germany approaches the issues by asking what a person skilled in the relevant subject matter of the patent would determine. Would that person consider the modification to be obvious and to result in the same effect? If so, then the two methods are equivalent and the new user is infringing.
    • Japan’s current law results in weak application of the doctrine of equivalents because the courts currently implement a number of different tests. If the substituted part is an essential part of the claim, then the accused device does not infringe; however, interchangeability is assessed at the time of manufacture.
  • Under any of these systems, basic cases of infringement, including minor and obvious substitutions of parts, will not allow infringing users to sidestep patent protection. However, in more complicated cases, the results will differ by location.
  • No system is clearly better or worse. Instead, the variety of different systems illustrates the difficulty in defining the scope of patent protection. To a large extent, this question is one of policy that is left to the individual jurisdictions.


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