Interpreting Claims in Canadian Patent Law: Purposive Construction and “Essential” Elements

In Canada, the anatomy of a patent (also known as the specification) consists of four parts: the abstract, the claims, the description and the drawings. Legally and commercially, the most important element is the claims – and a recent court decision has affirmed a long-standing approach on how to interpret patent claims.

The recently decided Benjamin Moore & Co. v Canada (Attorney General), 2022 FC 923 (“Benjamin Moore”) further affirmed the two highly influential decisions commenting on claims construction in Free World Trust c Électro Santé Inc, 2000 SCC 66 (“Free World Trust”) and Whirlpool Corp. v Camco Inc., 2000 SCC 67 (“Whirlpool”). These decisions emphasized the importance of “purposive construction” and interpreting claims with reference to their “essential” elements.

In Benjamin Moore, the Court pointedly rejected the “problem-solution” approach taken by the Canadian Intellectual Property Office wherein problems disclosed in patent applications were identified and the claims were construed in accordance with what elements would be essential to solving the identified problem.

In Whirlpool, the SCC described purposive construction as the “identification by the Court with the assistance of the skilled reader, of the particular words or phrases in the claims that describe what the inventor considered to be the ‘essential’ elements of his invention.” As stated in Free World Trust, it would be unfair to allow copycat inventions to elude patent monopolies simply because a competitor switched some of the “bells and whistles” from a patented invention.

Determining Whether an Element Is “Essential”

Whether an element is “essential” is a key consideration in any patent infringement dispute. If an allegedly infringing product or service contains all elements deemed to be essential in a patented invention, it will be found to infringe the patent. However, if a product or service is found to contain only non-essential elements of the patent, then the product or service has not infringed the patent.

To determine the “essential” elements of claims, the Supreme Court held that it is necessary to construe a patent as a whole, considering the entire anatomy of the patent, including the description. Furthermore, the Court held that claims construction should be determined from the point of view of a person skilled in the “art” of the particular field of invention (the “POSITA”). In most cases, claims construction is achieved by the courts with the assistance of experts.

In the context of the specific invention, the “non-essential” elements, as the term implies, are substitutable. When assessing whether an element is non-essential, the SCC stated in Free World Trust that the POSITA should consider whether an element could be substituted with a variant that would perform “substantially the same function in substantially the same way to obtain substantially the same result.” In other words, courts must ask, “Is the variant materially affected by the substitution?”

Following the reasons of Whirlpool and Free World Trust, Canadian courts have been guided to ask the following questions:

  1. Would the fact that the element could be substituted have been obvious to the POSITA at the patent’s publication date? If no, then the element is deemed to be essential. If yes, then –
  2. Would the POSITA have nonetheless understood from the language of the claims that the patentee intended for strict compliance with the claims? If yes, then the element is an essential element.

In Free World Trust, the SCC held that the public is entitled to “clear and definite” rules regarding the monopoly granted by a patent. On this basis, the SCC held that subjective or discretionary elements of claims interpretation, including the search for the “spirit of the invention,” should be minimized. To achieve predictability, courts must tie patentees to their claims; however, courts must also ensure that the claims are interpreted in an informed and purposive way.

To ensure informed construction of the claims, courts are normally assisted by expert witnesses who function as POSITAs. This provides comfort to patentees, as the technical terms and concepts within the claims will normally be read in the sense that the patentees intended. However, the public is entitled to rely upon the language of the claims interpreted fairly and knowledgeably, and where the inventor has misspoken or introduced unnecessarily limiting claims (i.e. narrower than what was actually invented), it is a “self-inflicted wound.”

When viewing a patent and constructing claims from the point of view of a POSITA, the whole disclosure must be reviewed. Even for words in the claims that “appear at first glance” to be unambiguous. Reference to the entire disclosure is necessary because certain words in the claims that seem simple, even to a POSITA, may have been meant by the inventor(s) to take on a specific meaning in the context of the invention.

The Takeaway

To determine the “essential” elements of patent claims, it is necessary that a patent’s entire specification be read by a POSITA. Whereas the POSITA varies widely depending on the complexity of the invention, unless you have familiarity with the field of the invention, you have little way of knowing what could be a technical term and therefore cannot determine the scope of the claims.

If you have questions regarding claims interpretation or would like to know more, please contact our patents and industrial designs team or see our blog series focused on intellectual property.

Note: This article is of a general nature only and is not exhaustive of all possible legal rights or remedies. In addition, laws may change over time and should be interpreted only in the context of particular circumstances such that these materials are not intended to be relied upon or taken as legal advice or opinion. Readers should consult a legal professional for specific advice in any particular situation.