IP monitor: Did you mean what you said? Overview of Section 53.1 of the Patent Act: Three years in



Canada Publication November 19, 2021

Nearly three years ago, section 53.1 of the Patent Act came into force, softening the ban on extrinsic evidence in claims construction in Canada (see our IP monitor of November 2018). This article provides an update on its interpretation and application over the past three years. While its interpretation continues to evolve, one trend is clear: its scope is limited.

The text of Section 53.1 

Section 53.1(1) reads, in part:

“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...”1 

The full text of section 53.1 can be found here.

The narrow interpretation of Section 53.1 

Over the past three years, Canadian federal courts have considered whether section 53.1 applies approximately 14 times. In half of those cases, the Federal Court (FC) found that section 53.1 was triggered. However, on appeal, the Federal Court of Appeal (FCA) restricted its application, overturning two of the cases, with three still pending appeal.

The FCA’s teachings thus far have restricted section 53.1 to an evidentiary rule. When section 53.1 was first introduced, many speculated that it would be akin to the file wrapper estoppel in the United States – a principle that prevents patent owners from broadening the scope of their patents to include elements that were previously forfeited through narrowing amendments to the patent application. This broad application, however, has not been adopted by the Canadian courts. Indeed, the FCA has noted that section 53.1 “does not refer to an estoppel.”2 Instead, based on the plain language of its text, section 53.1 is merely an evidentiary rule that may be triggered to admit limited correspondence between the patentee and the Canadian Patent Office in limited instances.       

Below are examples of its limited interpretation. 

Section 53.1 is only triggered when there are “inconsistent statements”

In Bauer Hockey Ltd. v Sport Maska Inc. (CCM Hockey), the FCA stated a patent’s prosecution history can only be admitted into evidence for the narrow purpose of rebutting “any representation made by the patentee in the action or proceeding as to the construction of a claim in the patent.”3 A particular representation must be identified before applying section 53.1: a representation made by the patentee during prosecution that is inconsistent with its position in the action.4  

The FCA’s interpretation in Bauer was more narrow than the one declared by the trial judge. At first instance, the FC held that section 53.1 applied whenever an issue of claims construction arose.5 On appeal, the FCA expressly rejected this interpretation, noting it “seems to open the door to unrestricted reference to the prosecution history.”6 The FCA further clarified that section 53.1’s purpose is “to provide a tool to use against patentees who take one position concerning the meaning of a claim during prosecution of a patent application and another during litigation on the resulting patent.”7    

An example of section 53.1 being triggered with an inconsistent statement arose in Eli Lilly Canada Inc. v Apotex Inc.8 In the action, the patentee asserted that an element was non-essential. During prosecution, however, the patentee had added it to the claim and deemed it “required” in order to overcome an obviousness objection.9 The FC applied section 53.1 and relied on the patent’s prosecution history to find that the claim was essential.10

Limited recourse to foreign prosecution history

Another way courts have limited the scope of section 53.1 is by narrowing the source of the inconsistent statement. That is, the inconsistent statement should come from a written communication between the patentee and the Canadian Patent Office, and not a communication with a foreign patent office.

The issue of whether section 53.1 allows recourse to a foreign file wrapper arose in Canmar Foods Ltd. v TA Foods Ltd.. At first instance, the FC stated that the language of section 53.1 is “limited to communications between the patentee and the Canadian Patent Office, and generally should be applied in that context.”11 However, the FC carved an exception for “extraordinary circumstances,”12 an example of such extraordinary circumstance being when the patentee refers to a corresponding foreign prosecution history in the Canadian file wrapper (such as the US application in Canmar). In these extraordinary circumstances, the court may look at the respective foreign prosecution history as part of a purposive construction of the claims.13  

On appeal, the FCA clawed back this exception and reiterated that section 53.1 specifically limits the communications to those with the Canadian Patent Office. On the specific facts, the FCA held that the FC should have refrained from considering the US prosecution history. There was nothing specific in the Canadian file wrapper that specifically incorporated the US prosecution history into the Canadian prosecution history. That said, the FCA stated that the question of “whether the doctrine of incorporation by reference should formally be treated as an exception to the general prohibition on foreign prosecution files, is a question best left for another day.”14 Therefore, the question of whether foreign prosecution history is ever admissible remains unanswered.   

Inconsistent statements must be made by the patentee or applicant, not a licensee

Section 53.1 is also limited in that it only applies to statements and representations made by a patentee or applicant, and not a licensee. A reminder that in Canadian law, a licensee is permitted to bring an action for patent infringement as a person claiming under the patentee. In Allergan Inc. v Sandoz Canada Inc., the FC held that if a licensee takes an inconsistent position as to the construction of a claim in the action compared to the patentee or applicant in prosecution, that will not trigger section 53.1.15 The court stated that the plain and ordinary meaning of section 53.1, together with a contextual reading of the Patent Act and jurisprudence, supported the position that “patentee” does not include a licensee.16


The introduction of section 53.1 into the Patent Act has allowed Canadian courts to consider a patent’s prosecution history during litigation. Since its enactment nearly three years ago, the FC and the FCA have considered and applied section 53.1 in a handful of cases. Below are some of the key takeaways from the case law.

  • Courts generally take a strict and narrow approach to section 53.1.
  • Prosecution history can only be used to rebut inconsistent statements; it cannot be used as an interpretive aid to claims construction in general.
  • There is limited recourse in relying on foreign prosecution history; however, the FCA has left the door open to it applying in certain circumstances. 
  • Section 53.1 applies only to statements and representations made by the applicant or the patentee, and does not include representations made by a licensee on behalf of the patentee.

Certain questions relating to the application of section 53.1 remain outstanding and require further clarification from the courts.

The authors wish to thank Marisa Kwan, articling student, for her help in preparing this IP monitor. 



Patent Act, s. 53.1(1).


Western Oilfield Equipment Rentals Ltd. v. M-I LLC, 2021 FCA 24 at para 19.


Bauer Hockey Ltd. v. Sport Maska Inc. (CCM Hockey), 2021 FCA 166 at para 36 [Bauer FCA]. As the text of section 53.1(1) states.


Bauer FCA at para 36. 


Bauer Hockey Ltd. v. Sport Maska Inc. (CCM Hockey), 2020 FC 624 at para 65 [Bauer FC].


Bauer FCA at para 36.


Bauer FCA at para 37.


Eli Lilly Canada Inc. v. Apotex Inc., 2020 FC 814 [Eli Lilly].


Eli Lilly at para 175.


Eli Lilly at para 176. 


Canmar Foods Ltd. v. TA Foods Ltd., 2019 FC 1233 at para 70 [Canmar FC]. 


Canmar FC at para 73.


Canmar FC at paras 70-73. A more in-depth analysis of the FC’s Canmar decision can be found in our IP monitor of October 2019.


Canmar Foods Ltd. v. TA Foods Ltd., 2021 FCA 7 at para 74.


 Allergan Inc. v. Sandoz Canada Inc., 2020 FC 1189 [Allergan]. A notice of appeal has been filed.


Allergan at para 133.

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