Is File History Estoppel Coming to Canada?

The use of patent prosecution history is a standard part of analysing patents in the United States but the courts in Canada have resisted using the prosecution history for parsing the words of patent claims. A recent decision highlights a situation where the use of the patent prosecution history would have resulted in a different analysis in Canada and the trial judge asks whether it is time to consider the prosecution history and imposing consequences on parties that argue differently at court than before the patent office.

During the patent filing process, the applicant, through their patent agent, often makes amendments to the patent application and makes arguments to the patent office about the meaning of terms and how the invention can be distinguished from prior art. The communications back and forth between the patent agent and the patent office, called the prosecution file, is public and these days often available online through the patent office.

In the United States, it is standard for the court to consider statements made by the applicant about the meaning of terms used in the claims and the scope of the invention when considering what the patent means for the purpose of validity and infringement.

In contrast in Canada, the Supreme Court in 2000 held that ‘extrinsic’ material, including the prosecution history of the patent, was not to be considered for claim construction, i.e. determining what the words of the patent mean. Justice Ian Binnie stated the following in Free World Trust v. Électro Santé Inc., 2000 SCC 66 at para 66:

In my view, those references to the inventor’s intention refer to an objective manifestation of that intent in the patent claims, as interpreted by the person skilled in the art, and do not contemplate extrinsic evidence such as statements or admissions made in the course of patent prosecution. To allow such extrinsic evidence for the purpose of defining the monopoly would undermine the public notice function of the claims, and increase uncertainty as well as fuelling the already overheated engines of patent litigation. The current emphasis on purposive construction, which keeps the focus on the language of the claims, seems also to be inconsistent with opening the pandora’s box of file wrapper estoppel. If significant representations are made to the Patent Office touching the scope of the claims, the Patent Office should insist where necessary on an amendment to the claims to reflect the representation.

In Pollard v. Scientific Games, 2016 FC 883, a decision released in July after a trial in which I was involved, Justice Locke had to deal with this issue directly when the prosecution history pointed to one meaning for the word ‘continuous’ in the patent claim but the patent owner was arguing a different meaning during the trial. During prosecution, the applicant had argued that the word continuous served to distinguish the invention from the prior art.

While the judge stated that he did not consider the file history at all when construing the meaning of the word ‘continuous’ the judge commented that if the file history was considered, such as it would in the United States, a different construction of the term would have been used:

[238] I would expect that [the patentee’s] argument would never have made it to a trial in the US where the principle of file wrapper estoppel applies. There, [the patentee] would likely not have been allowed to argue a claim construction that attempts to recapture ground conceded during prosecution of the patent application to avoid prior art.

[239] This case highlights a potential risk in taking a simpler approach to claim construction by ignoring extrinsic evidence, such as the prosecution history of the patent in suit. As revealed in my analysis above, excluding such extrinsic evidence resulted in a very different construction of the phrase “a removable continuous scratch-off coating covering both the printed indicia in said play area and the bar code” than would otherwise have been the case.

Instead of looking to the patent file history, the claim term was analyzed by the court from the perspective of the person skilled in the art looking only at the patent (but not the prosecution history). At paragraph 80, Justice Locke asked, “whether it is time to revisit the rule against using extrinsic evidence in claim construction.”

Assuming the Canadian courts continue to exclude consideration of the patent prosecution when construing claim terms, it is possible for courts in the United States and Canada to come to opposite conclusions on the meaning of claim terms even if the patents are the same.

Several years ago, Justice de Montigny was faced with the arguments about using the file history to understand the patent in Distrimedic Inc. v. Dispill Inc., 2013 FC 1043. Justice de Montigny permitted some use of the file history to be used to assist with determining whether a claim feature was essential. Justice de Montigny wrote at paragraph 210:

While statements or admissions made in the course of patent prosecution shall not be used for the purpose of interpreting a claim, this is not what the Court is called upon to do in the case at bar. A change in the wording of a claim as a result of an objection from the Patent Office is an objective fact from which an inference may be drawn, and is not the same as representations made to the Patent Office. A purposive construction should obviously focus on the wording of a claim, obviously, but this is a far cry from saying that nothing else should be considered.

Similarly, Justice de Montigny considered the file history in Eli Lilly Canada Inc. v. Mylan Pharmaceuticals ULC, 2015 FC 125 at paragraph 154, to assist with determining whether a feature was an instruction on how to administer a dosage or an aspect of the dosage form itself for determining whether a claim was patentable subject matter or a method medical treatment.

Also in the last couple of years, Justice Mosley, in NOV Downhole Eurasia Limited v. TLL Oil Field Consulting, 2014 FC 889, considered whether a pleading ought to be struck that referred to the file history to defend against infringement arguing that a feature added during prosecution and appearing in each of the claims did not exist in their device. The defendant argued that the allegations were grounded in section 53(1) and so should not be struck. The court dismissed the motion to strike as there was a chance of success on the issue.

These cases show how the prosecution history, even if not directly citable, can be helpful on issues involving patent validity, construction and infringement. Parties will likely be relying on these decisions to press the courts to find more exceptions for using the file history at trial. These developments also put pressure on patent agents to be careful with amendments and arguments made during the prosecution process. Patent lawyers will be watching how this developments and whether the courts accept Justice Locke’s invitation to revisit file wrapper estoppel in Canada.


  1. David Collier-Brown

    Goodness, from a public-policy standpoint, the persons arguing the case should be entitled to use any non-privileged information that the court accepts as evidence. I’m surprised the claims have to be considered in a way that (emotionally) sounds more like the Quebec civil law system than the British…