In its recent decision in Bauer Hockey Ltd. v Sport Maska Inc. (CCM Hockey), the Federal Court considered prosecution history as an aid to construing a patent 1. This is only the second time the Court has considered this issue since amendments to the Patent Act regarding the treatment of prosecution history were made in late 2018. This bulletin discusses the implications of Bauer, as well as the first decision on this issue, Canmar Foods Ltd v TA Foods Ltd2.

What you need to know

  • While "prosecution history estoppel" (or "file wrapper estoppel") exists as a rule of evidence in the United States, changes to the Canadian Patent Act have created a similar (but not analogous) rule that permits a court to consider the prosecution history as an element of claim construction.
  • Statements made during the prosecution of a patent can be used against a patentee in subsequent patent litigation.
  • The implication of this conclusion is that the patentee must take care in ensuring consistency in the positions taken during prosecution.

Bauer: prosecution history and its effect on claims construction

In May 2020, the Federal Court dismissed an action for infringement brought by Bauer against a rival hockey skate manufacturer, finding the patent-in-suit to be invalid. One of the central issues in the case was the role statements made during the prosecution of the patent played in construing the claims.

Until section 53.1 of the Patent Act was added in 2018, the prosecution history of a patent was inadmissible under Canadian law3. Section 53.1 provides that written communications made by a patentee to the Canadian Intellectual Property Office during the prosecution of a patent are admissible in a subsequent proceeding to aid in the construction of the patent's claims:

53.1 (1) In any action or proceeding respecting a patent, a written communication, or any part of such a communication, may be admitted into evidence to rebut any representation made by the patentee in the action or proceeding as to the construction of a claim in the patent if

  1. it is prepared in respect of
    1. the prosecution of the application for the patent,
    2. a disclaimer made in respect of the patent, or
    3. a request for re-examination, or a re-examination proceeding, in respect of the patent; and
  2. it is between
    1. the applicant for the patent or the patentee; and
    2. the Commissioner, an officer or employee of the Patent Office or a member of a re-examination board.

In Bauer, the Court (Justice Grammond) explained that, like all legislation, section 53.1 should be given a large, liberal and purposive interpretation. The Court found that the purpose of section 53.1 was to avoid the mischief that arises when a patentee "argue[s] a claim construction that attempts to recapture ground conceded during prosecution of the patent application to avoid prior art." In light of section 53.1, purposive construction goes beyond consideration of the patent claims and disclosure: it also requires consideration of the substance behind intentional amendments to the claims issued in Canadian patents.

The Court observed that when an issue of claims construction arises, the patentee is always "making representations to the Court as to the proper construction of the claims and the defendant is always attempting to rebut those representations." Therefore, in the Court's view, as long as the issue is one of claims construction, section 53.1 applies: prosecution history is admissible, full stop. In the words of Justice Grammond: "[T]here is no need to identify a particular representation and rebuttal every time a reference is made to the prosecution history. It is simply integrated in the interpretive process."

Practitioners in the area are aware that the use of a prosecution history is described as an evidentiary rule of estoppel in the United States, and it can be used to "estop" or prevent a patentee from taking a position in Court inconsistent with that given in the patent office during the prosecution of the patent. The Court in Bauer clarified that in Canada, section 53.1 squarely makes this a matter of claims construction.

Canmar: the role of foreign prosecution histories in Canadian litigation

In Canmar, Justice Manson considered the prosecution history of a U.S. patent application during which limitations were added to overcome prior art cited by the U.S. Patent and Trademark Office.

The Court noted that section 53.1 makes no reference to prosecution histories from other jurisdictions. The provision is therefore generally limited to using Canadian prosecution file histories to rebut any position taken on claim construction. Absent extraordinary circumstances, histories from other jurisdictions remain inadmissible for the purposes of construing terms used in Canadian patents.

However, where a patentee, during the prosecution of a patent in Canada, has specifically referred to the prosecution history of the patent in a foreign jurisdiction and acknowledged why intentional amendments to limit the claims were made (i.e., to overcome novelty and obviousness objections), the Court may look at the foreign prosecution history as part of a purposive construction of the claims of the Canadian patent.

This is precisely what occurred in Canmar, where the Court looked to the U.S. prosecution history to assist its claims construction analysis because that prosecution history had been incorporated by reference in the Canadian application.

Implications for prosecution history in Canada

Following Canmar and Bauer, statements made during the prosecution of a patent in Canada and, in some circumstances, statements made in foreign patent applications may be used to construe a patent. As parties prosecute and litigate patents, they should be aware that the prosecution history may inform the ultimate construction of the patent, such that ground conceded during prosecution may not be recovered during litigation. Careful attention should be paid to statements made and to statements incorporating by reference the prosecution history of foreign patents, as such statements may import foreign prosecution history into the interpretation of the Canadian patent's claims in subsequent litigation.


1. 2020 FC 624.

2. 2019 FC 1233.

3. Free World Trust v Électro Santé Inc, 2000 SCC 66, para. 66.

Originally published on May 22 2020

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.