Invention, Refinement and Patent Claim Scope: A New Perspective on the Doctrine of Equivalents

67 Pages Posted: 20 Apr 2004 Last revised: 15 Feb 2015

Michael J. Meurer

Boston University - School of Law

Craig Allen Nard

Case Western Reserve University School of Law


The doctrine of equivalents (DOE) allows courts to expand the scope of patent rights granted by the Patent Office. The doctrine has been justified on fairness grounds, but it lacks a convincing economic justification. The standard economic justification holds that certain frictions block patent applicants from literally claiming appropriately broad rights, and thus, the DOE is available at trial to expand patent scope and overcome these frictions. The friction theory suffers from three main weaknesses. First, the theory is implausible on empirical grounds. Frictions such as limits of language, mistake, and unforeseeability are missing from the leading cases. Second, there is not a convincing answer to the question of why the doctrine of equivalents, rather than some other doctrinal approach, should be used to overcome the frictions. The frictions can be overcome, or at least mitigated, for example, by astutely amending claims during prosecution; through a reissue proceeding after the patent issues; or through artful claim drafting as an initial matter. Third, proponents of a far-reaching DOE fail to pay adequate attention to the notice function of patent claims and are insufficiently sensitive to patent law's delicate incentive dynamic.

We develop a better explanation of why claim breadth falls short of the maximum breadth allowed by patent law. Our explanation replaces the passive patent attorney depicted in the friction theory with an active inventor and attorney who are capable of responding effectively to the frictions mentioned above. Whether an inventor obtains the broadest permissible claim breadth depends mostly on the talent and effort of the inventor and attorney in identifying what has been enabled. A good attorney predicts the embodiments that could be chosen by infringers and finds appropriate language to draft a suitably broad claim. We call this process claim refinement, and we develop a refinement theory of the doctrine of equivalents.

We justify the doctrine of equivalents primarily as a tool for promoting efficient investment in claim refinement. Although critics of the DOE contend the doctrine unduly inhibits competition, we show the degree of competition is often unaffected by the presence or absence of the DOE. The inventor can block competition in the absence of the DOE by drafting broad patent claims. The DOE should be used to avoid socially wasteful preemptive refinement. We reject the popular notion that the DOE is especially appropriate in the case of unforeseeable, later-developed technology. We reach this conclusion because in certain cases patent applicants can capture unforeseen embodiments at relatively low cost through clever claim drafting strategies. And in other cases unforeseen equivalents are unattainable no matter the amount of time and money spent on refinement efforts. In the latter cases, patent applicants would not exert much effort refining their claims to cover these equivalents, and inventor's incentives would not be much affected by a minute probability of loss of effective patent protection.

Keywords: patent scope, invention, doctrine of equivalents, patent claims

JEL Classification: K2, L5, O34

Suggested Citation

Meurer, Michael J. and Nard, Craig Allen, Invention, Refinement and Patent Claim Scope: A New Perspective on the Doctrine of Equivalents. Boston Univ. School of Law Working Paper No. 04-03; Georgetown Law Journal, Vol. 93, 2005; Case Legal Studies Research Paper No. 04-5. Available at SSRN: or

Michael J. Meurer (Contact Author)

Boston University - School of Law ( email )

765 Commonwealth Avenue
Boston, MA 02215
United States
617-353-6292 (Phone)
617-353-3077 (Fax)

Craig Allen Nard

Case Western Reserve University School of Law ( email )

11075 East Boulevard
Cleveland, OH 44106-7148
United States
216-368-6348 (Phone)
216-368-2086 (Fax)


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