Canada’s Intellectual Property Firm

Claim indefiniteness in Canada: An overview for U.S. practitioners

Authored byChristopher Thompson

This summer, the U.S. Supreme Court issued an important ruling in Nautilus Inc v Biosig Instruments Inc134 S. Ct. 2120, 110 U.S.P.Q.2d 1688 (2014) (“Nautilus”), restating the appropriate test for assessing whether a claim is indefinite. In light of this recent change in law, it is worth reflecting on the differences between the current approaches to indefiniteness applied in the U.S. and Canada, as these differences may be of strategic value when planning a litigation strategy against cross-border infringers.

Claim indefiniteness in the U.S.

Prior to Nautilus, the prevailing test for indefiniteness, i.e., claim ambiguity, had been based on a line of decisions holding that a claim would not be indefinite unless it is “not amenable to construction” or “insolubly ambiguous”. In the unanimous ruling in Nautilus, the U.S. Supreme Court substituted a test based on reasonable certainty in the eyes of the skilled person, namely: “a patent is invalid for indefiniteness if its claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention” (Nautilus at p. 1). Although it remains to be seen precisely how the new test for indefiniteness will be applied by the U.S. Courts, it is likely that it may be easier to invalidate patent claims for indefiniteness under this new standard.

Claim indefiniteness in Canada versus the U.S.

As a first point of distinction with Canadian practice, it is worthwhile noting that in Canadian practice there is no equivalent to a U.S. Markman hearing, in which claim construction is performed as a preliminary step prior to a trial on the merits of claim validity and infringement (Realsearch Inc v Valon Kone Brunette Ltd2004 FCA 5). This may allow accused infringers to assert an indefiniteness defence at an earlier stage than would be possible in Canada. For example, at the District Court level in Nautilus, the defendant had successfully moved for summary judgment immediately after the Markman hearing. In contrast, in Canadian litigation, claim indefiniteness would most likely be addressed at trial at the same time as all other construction, infringement and validity issues, which may influence the litigation tactics and settlement positions of both the patentee and defendant in cases where indefiniteness arguments are raised.

It is also important to note that, unlike U.S. practice, statements made to the Canadian patent office during prosecution (or statements made in the prosecution of other related foreign applications), are typically inadmissible for the purpose of claim construction in Canada. For this reason, if there are potentially problematic statements on the record that have subsequently been discovered to have been inadvertently erroneous and which might potentially attract an indefiniteness attack in the U.S., Canada may represent a more attractive jurisdiction for patent enforcement.

Another point of distinction with Canadian practice relates to the proper date used for assessing indefiniteness. In Nautilus, the Court reiterated that indefiniteness is measured from the viewpoint of a skilled person at the time the patent was filed (Nautilus at p. 9). In Canada, the proper date for assessing indefiniteness is the date of publication (Alcon Canada Inc v Cobalt Pharmaceuticals Co2014 FC 149 (“Alcon”) at para. 236). For some technologies, the difference in relevant knowledge between filing and publication could materially affect construction, and consequently the assessment as to whether claims are indefinite.

As for the actual test for indefiniteness applied in Canada (which is often referred to as claim ambiguity in Canadian jurisprudence), there is no single test that reappears consistently in the case law. However, broadly speaking, provided that the subject matter of a claim can be assigned a meaning that would be understood by a person skilled in the art, when read with “a mind willing to understand, not a mind desirous of misunderstanding”, a claim is not indefinite (Whirlpool Corp v Camco Inc2000 SCC 67 at para 49). In particular, there is no requirement that the claims be “a model of concision and lucidity” and provided that a patent claim can be understood “using grammatical rules and common sense, it cannot be ambiguous” (Alcon at para 232). Generally, the Courts take the view that there will be “few instances where the imprecision of a claim serves to invalidate the claim”, (Alcon at para 232) and that indefiniteness is to be a “last resort, rarely, if ever, to be used” (Pfizer Canada Inc v (Minister of Health)2005 FC 1725 at para 53). For these reasons, it is perhaps most appropriate to characterize the Canadian approach to indefiniteness as being broadly similar to the test applied in the U.S. prior to Nautilus.

The distinctions between the Canadian approach to claim indefiniteness and the approach articulated by the U.S. Supreme Court in Nautilus are perhaps best illustrated by considering one of the core construction issues in Nautilus. In that case, the claims referred to a “spaced relationship” between two electrodes. It was alleged, and accepted by the District Court, that the patent claims “did not tell [the court] or anyone what precisely the space should be” or supply “any parameters” for determining the appropriate spacing. However, the patentee had argued that the bounds of the term “spaced relationship” required for the invention to work would be implicitly understood by a skilled person.

In Canada, when faced with similar situations where some level of technical knowledge of the skilled person must be imported into a patent claim during the construction process in order to prevent a claim from being indefinite, the Courts have been willing to favour a construction which upholds the patent. For example, in one case, the Court noted that: “If there is more than one construction that can be reasonably reached, the Court must favour the construction which upholds the patent. Where the language of the specification, upon a reasonable view of it, can be read so as to afford the inventor protection for that which he has actually in good faith invented, the court, as a rule, will endeavour to give effect to that construction” (Letourneau v Clearbrook Iron Works Ltd2005 FC 1229 at para. 38). This approach appears to differ from Nautilus where Justice Ginsburg suggested that if a claim term “is open to multiple interpretations reflecting markedly different understandings of the patent’s scope”, this may be an indication of indefiniteness (Nautilus at pp. 13–14).


Time will tell how the change to law arising from Nautilus will affect practice. Based on existing jurisprudence, it can be expected that Canadian courts will apply a more lenient approach to indefiniteness, in which case there may be strategic advantages for patentees to consider Canada as a jurisdiction for patent enforcement where indefiniteness is expected to be an issue.

For further information, please contact a member of our firm’s Litigation group.

The preceding is intended as a timely update on Canadian intellectual property and technology law. The content is informational only and does not constitute legal or professional advice. To obtain such advice, please communicate with our offices directly.