Overbreadth: Don’t Let Your Patent Specification Hold Your Claims Back


October 22, 2021

In Canada, defendants in patent infringement proceedings often plead that the asserted claims are invalid for being overbroad. The doctrine of overbreadth (sometimes referred to as “covetous claiming”) stems from the bargain at the heart of the patent system; it seeks to limit claims to only the invention disclosed to the public in the specification. The doctrine of overbreadth applies where claims are directed to (a) more than is described in a patent, or (b) more than the inventor has invented.

Over the years, overbreadth has been only rarely used to decide cases as the courts have typically applied other pleaded grounds of invalidity to dispose of the cases before them.

In a recent decision, Seedlings Life Science Ventures, LLC v. Pfizer Canada ULC (“Seedlings”), the Federal Court of Appeal addressed both (a) whether overbreadth is a proper ground for invalidity and, (b) if so, under what circumstances is a patent claim invalid for overbreadth.

Is Overbreadth a Proper Ground of Invalidity?

In Seedlings, the patentee argued that the overbreadth doctrine is not a ground of invalidity that should be recognized by law. First, the patentee argued that there is no statutory basis for overbreadth: the requirements for a valid patent are set out in the Patent Act and nothing in the statute relates to overbreadth. Second, it argued that the only other Canadian case in which a patent claim was held invalid solely on the ground of overbreadth, Amfac Foods v. Irving Pulp & Paper (“Amfac”) was wrongly decided. Third, it argued that the trial judge’s finding of overbreadth in the case under appeal was an improper re-emergence of the “promise doctrine” which had been rejected by the Supreme Court of Canada in AstraZeneca Canada v. Apotex Inc. (“AstraZeneca”). The so-called “promise doctrine” had, until being struck down by the Supreme Court, dictated that a patent was invalid for lack of utility if the specification promised more than the patented invention could provide.

The Federal Court of Appeal dismissed the patentee’s arguments. On the first point, it found that the Patent Act’s requirements that a patent specification correctly and fully describe the invention and that the claims define distinctly and in explicit terms the subject-matter of the invention provide a sufficient statutory basis for the doctrine of overbreadth. On the second point, Amfac was implicitly endorsed, and on the third point the Federal Court of Appeal quickly dismissed the argument that overbreadth was an improper extension of the promise doctrine by noting that the Supreme Court’s decision in AstraZeneca contained the statement that “[a]n overly broad claim may be declared invalid.”

Application of the Doctrine of Overbreadth

The Court of Appeal acknowledged that the doctrine of overbreadth is difficult to apply and often overlaps with other grounds of invalidity. For example, a claim that is invalid for anticipation because it encompasses embodiments that are described in the prior art may also be considered overbroad because it claims more than the inventor truly invented. However, the Court refused to shy away from applying the doctrine notwithstanding these difficulties.

The Court found that the doctrine of overbreadth is not to be limited by rules prohibiting recourse to the disclosure to construe claims. For example, in determining whether a patent claim is invalid for overbreadth, it is permissible to review the disclosure to determine which features are “so key” (alternatively referred to as core features) to the invention that their omission from the claims is not contemplated. Determining core features may include determining the difficulty of replacing features in the disclosure, or whether the invention if modified would work differently.

Evidence Which Sustains a Finding of Overbreadth

The Federal Court of Appeal next discussed the trial judge’s three reasons for finding the disputed claims to be invalid for overbreadth, namely that:

  • the omitted elements are shown in all of the embodiments;
  • the omitted elements interact with one another and are at the core of the mechanism of the device in that the device would work differently if they were replaced and replacing them would require inventive ingenuity; and
  • the omitted elements and their arrangement are entirely original.

The appellate court quite rightly held that the first and third reasons would, without more, be inadequate to establish overbreadth since it would be improper to limit an invention to the preferred embodiments described in a patent or to require that all original elements described in a patent be claimed.

The second reason applied by the trial judge was found to best reflect the principle behind overbreadth. Reviewing the trial judge’s decision, the Court of Appeal first identified the core of the invention by reviewing the shortcomings of the prior art identified in the patent application. The trial judge’s findings of fact, including that:

  • the patent did not describe how to make the invention without the omitted elements; and
  • the evidence revealed that the person skilled in the art of the patent would not know how to make the invention without the omitted elements,

were sufficient to ground a finding of invalidity based on overbreadth as a result of the claims not including the core of the invention (i.e., claiming more than was invented). Overbreadth did not follow from the finding that the omitted elements were described in all of the embodiments.

In the end, the court was satisfied that the trial judge had not made a palpable and overriding error in deciding that, based on the above evidence, the claims were invalid for overbreadth.

Additional Considerations

The doctrine of overbreadth can lead to different results when applied to different claim types within the same patent. In AFD Petroleum Ltd. v. Frac Shack Inc., the appellant alleged that method claims related to a fuel delivery system were overbroad as they omitted the location of valves in the system. The Federal Court of Appeal found that valve placement was an essential element of the disclosed system but noted that the essential elements of the claimed method were not necessarily the same. The method claim was permitted to be broader and to have different essential elements (at para. 55). Ultimately, the Court of Appeal found that the omission in the method claims of a reference to the valve placement did not render the claims in dispute invalid for overbreadth.

The doctrine of overbreadth is also not to be applied in a manner that ignores common sense. For example, the decision of the Supreme Court of Canada in Burton Parsons v Hewlett Packard Ltd, is often cited for the proposition that claims are not overly broad where the person of ordinary skill in the art of the patent would know to avoid known unsuitable choices (see, for example Astrazeneca Canada Inc. v. Apotex Inc., at para. 277)

Implications Going Forward

The Federal Court of Appeal’s decision in Seedlings has removed any doubt regarding whether overbreadth is a proper ground of invalidity. Therefore, defendants in litigation would be well advised to consider pleading overbreadth as a ground of invalidity where it is supported by the facts.

Additionally, patent agents will want to keep the doctrine in mind when drafting applications. For example, it would be advisable to avoid making any statements in a patent application that would give the false impression that a particular element is essential to the practice of an invention. Statements identifying difficulties in the prior art should be scrutinized to avoid a court reading in essential elements to solve the identified difficulties. Additionally, if an inventor wishes to claim a particular variation of the invention that is not disclosed in any of the embodiments, it may be necessary to include text in the specification regarding how the variation can be practised.


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