Canada: Claim Indefiniteness In Canada: An Overview For U.S. Practitioners

This summer, the U.S. Supreme Court issued an important ruling in Nautilus Inc v Biosig Instruments Inc, 134 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 U.S. 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, in the U.S. 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 U.S. 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 Ltd, 2004 FCA 5). This may allow accused infringers in the U.S. to assert an indefiniteness defense 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 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 Co, 2014 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 Inc, 2000 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 Canada (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 Ltd, 2005 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 U.S. law arising from Nautilus will affect U.S. 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.

To print this article, all you need is to be registered on

Click to Login as an existing user or Register so you can print this article.

In association with
Related Topics
Related Articles
Related Video
Up-coming Events Search
Font Size:
Mondaq on Twitter
Register for Access and our Free Biweekly Alert for
This service is completely free. Access 250,000 archived articles from 100+ countries and get a personalised email twice a week covering developments (and yes, our lawyers like to think you’ve read our Disclaimer).
Email Address
Company Name
Confirm Password
Mondaq Topics -- Select your Interests
 Law Performance
 Law Practice
 Media & IT
 Real Estate
 Wealth Mgt
Asia Pacific
European Union
Latin America
Middle East
United States
Worldwide Updates
Registration (you must scroll down to set your data preferences)

Mondaq Ltd requires you to register and provide information that personally identifies you, including your content preferences, for three primary purposes (full details of Mondaq’s use of your personal data can be found in our Privacy and Cookies Notice):

  • To allow you to personalize the Mondaq websites you are visiting to show content ("Content") relevant to your interests.
  • To enable features such as password reminder, news alerts, email a colleague, and linking from Mondaq (and its affiliate sites) to your website.
  • To produce demographic feedback for our content providers ("Contributors") who contribute Content for free for your use.

Mondaq hopes that our registered users will support us in maintaining our free to view business model by consenting to our use of your personal data as described below.

Mondaq has a "free to view" business model. Our services are paid for by Contributors in exchange for Mondaq providing them with access to information about who accesses their content. Once personal data is transferred to our Contributors they become a data controller of this personal data. They use it to measure the response that their articles are receiving, as a form of market research. They may also use it to provide Mondaq users with information about their products and services.

Details of each Contributor to which your personal data will be transferred is clearly stated within the Content that you access. For full details of how this Contributor will use your personal data, you should review the Contributor’s own Privacy Notice.

Please indicate your preference below:

Yes, I am happy to support Mondaq in maintaining its free to view business model by agreeing to allow Mondaq to share my personal data with Contributors whose Content I access
No, I do not want Mondaq to share my personal data with Contributors

Also please let us know whether you are happy to receive communications promoting products and services offered by Mondaq:

Yes, I am happy to received promotional communications from Mondaq
No, please do not send me promotional communications from Mondaq
Terms & Conditions (the Website) is owned and managed by Mondaq Ltd (Mondaq). Mondaq grants you a non-exclusive, revocable licence to access the Website and associated services, such as the Mondaq News Alerts (Services), subject to and in consideration of your compliance with the following terms and conditions of use (Terms). Your use of the Website and/or Services constitutes your agreement to the Terms. Mondaq may terminate your use of the Website and Services if you are in breach of these Terms or if Mondaq decides to terminate the licence granted hereunder for any reason whatsoever.

Use of

To Use you must be: eighteen (18) years old or over; legally capable of entering into binding contracts; and not in any way prohibited by the applicable law to enter into these Terms in the jurisdiction which you are currently located.

You may use the Website as an unregistered user, however, you are required to register as a user if you wish to read the full text of the Content or to receive the Services.

You may not modify, publish, transmit, transfer or sell, reproduce, create derivative works from, distribute, perform, link, display, or in any way exploit any of the Content, in whole or in part, except as expressly permitted in these Terms or with the prior written consent of Mondaq. You may not use electronic or other means to extract details or information from the Content. Nor shall you extract information about users or Contributors in order to offer them any services or products.

In your use of the Website and/or Services you shall: comply with all applicable laws, regulations, directives and legislations which apply to your Use of the Website and/or Services in whatever country you are physically located including without limitation any and all consumer law, export control laws and regulations; provide to us true, correct and accurate information and promptly inform us in the event that any information that you have provided to us changes or becomes inaccurate; notify Mondaq immediately of any circumstances where you have reason to believe that any Intellectual Property Rights or any other rights of any third party may have been infringed; co-operate with reasonable security or other checks or requests for information made by Mondaq from time to time; and at all times be fully liable for the breach of any of these Terms by a third party using your login details to access the Website and/or Services

however, you shall not: do anything likely to impair, interfere with or damage or cause harm or distress to any persons, or the network; do anything that will infringe any Intellectual Property Rights or other rights of Mondaq or any third party; or use the Website, Services and/or Content otherwise than in accordance with these Terms; use any trade marks or service marks of Mondaq or the Contributors, or do anything which may be seen to take unfair advantage of the reputation and goodwill of Mondaq or the Contributors, or the Website, Services and/or Content.

Mondaq reserves the right, in its sole discretion, to take any action that it deems necessary and appropriate in the event it considers that there is a breach or threatened breach of the Terms.

Mondaq’s Rights and Obligations

Unless otherwise expressly set out to the contrary, nothing in these Terms shall serve to transfer from Mondaq to you, any Intellectual Property Rights owned by and/or licensed to Mondaq and all rights, title and interest in and to such Intellectual Property Rights will remain exclusively with Mondaq and/or its licensors.

Mondaq shall use its reasonable endeavours to make the Website and Services available to you at all times, but we cannot guarantee an uninterrupted and fault free service.

Mondaq reserves the right to make changes to the services and/or the Website or part thereof, from time to time, and we may add, remove, modify and/or vary any elements of features and functionalities of the Website or the services.

Mondaq also reserves the right from time to time to monitor your Use of the Website and/or services.


The Content is general information only. It is not intended to constitute legal advice or seek to be the complete and comprehensive statement of the law, nor is it intended to address your specific requirements or provide advice on which reliance should be placed. Mondaq and/or its Contributors and other suppliers make no representations about the suitability of the information contained in the Content for any purpose. All Content provided "as is" without warranty of any kind. Mondaq and/or its Contributors and other suppliers hereby exclude and disclaim all representations, warranties or guarantees with regard to the Content, including all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement. To the maximum extent permitted by law, Mondaq expressly excludes all representations, warranties, obligations, and liabilities arising out of or in connection with all Content. In no event shall Mondaq and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use of the Content or performance of Mondaq’s Services.


Mondaq may alter or amend these Terms by amending them on the Website. By continuing to Use the Services and/or the Website after such amendment, you will be deemed to have accepted any amendment to these Terms.

These Terms shall be governed by and construed in accordance with the laws of England and Wales and you irrevocably submit to the exclusive jurisdiction of the courts of England and Wales to settle any dispute which may arise out of or in connection with these Terms. If you live outside the United Kingdom, English law shall apply only to the extent that English law shall not deprive you of any legal protection accorded in accordance with the law of the place where you are habitually resident ("Local Law"). In the event English law deprives you of any legal protection which is accorded to you under Local Law, then these terms shall be governed by Local Law and any dispute or claim arising out of or in connection with these Terms shall be subject to the non-exclusive jurisdiction of the courts where you are habitually resident.

You may print and keep a copy of these Terms, which form the entire agreement between you and Mondaq and supersede any other communications or advertising in respect of the Service and/or the Website.

No delay in exercising or non-exercise by you and/or Mondaq of any of its rights under or in connection with these Terms shall operate as a waiver or release of each of your or Mondaq’s right. Rather, any such waiver or release must be specifically granted in writing signed by the party granting it.

If any part of these Terms is held unenforceable, that part shall be enforced to the maximum extent permissible so as to give effect to the intent of the parties, and the Terms shall continue in full force and effect.

Mondaq shall not incur any liability to you on account of any loss or damage resulting from any delay or failure to perform all or any part of these Terms if such delay or failure is caused, in whole or in part, by events, occurrences, or causes beyond the control of Mondaq. Such events, occurrences or causes will include, without limitation, acts of God, strikes, lockouts, server and network failure, riots, acts of war, earthquakes, fire and explosions.

By clicking Register you state you have read and agree to our Terms and Conditions