Notes to Patent Drafters: Common Issues with Broad Specifications in Canada


The Canadian Patent Act imposes an unyielding relationship between the requirement for a written description of the invention and claims for which patent protection is sought. A patent specification must be sufficient to allow the full scope of the claimed invention to be practiced, without the need for additional inventive ingenuity. The desire to claim broadly means that patent applicants will attempt to claim outside the specific embodiments which exemplify the invention.  However, an applicant must not claim more than they have actually invented or more than what is disclosed in the description.  As the Federal Court of Appeal stated: “It is now settled law that a patent which claims more than what was invented or disclosed can be found invalid for being overly broad.”

Adequate Written Description

The requirement that the full breadth of a claim must be supported by the description provides particular hurdles for claims related to biomolecules, which are typically claimed by structure and also by function.  Functional limitations are permissible if the person skilled in the art would not need to resort to inventive ingenuity to practice the full scope of the claim. For example, a claim to “a plant transformation vector comprising a gene of interest; a transposon; and a marker gene positioned within the transposon, wherein the marker gene induces abnormal cellular differentiation in plant tissue” will be adequately supported in the description if at least one example is described, and it is established that marker genes are well known in the prior art by persons skilled in the art.

The scope of the functional limitation must be supported by a suitable number of representative species.  Broader scope obviously requires a greater number of representative species to be described.  On the other hand, where the use of functional language requires an inventive effort to practice the full scope of the claim, or the functional limitation is itself overly broad, the claim may be invalid even if a representative species is described.  Test data which illuminates the function of representative species and structure-function relationships may go a long ways to providing adequate written description support.

The Supreme Court has stated that a skilled reader should not have to engage in even a minor research project in order to determine the bounds of an invention; however, this does leave open the possibility that some trial and error may be permitted. The identification of a simple problem and the application of what is a routine modification in testing protocols are viewed as being a matter of simple trial and error, and not a “research project”. This means that routine experimentation is permissible, so long as it falls short of being a research project and not critical to the understanding or practice of the invention.

That said, wherever possible drafters should avoid requiring the skilled reader to conduct trial and error in order to make use of the invention, as this runs the risk of invalidating the patent for insufficient disclosure.

In the specific case of antibodies, Canadian law is now more permissive than in other jurisdictions, notably the United States, as a result of a recognition of the evolving state-of-the-art.  In Re Immunex, a working example of a monoclonal antibody was found not to be necessary when there is a direct structural relationship and specific reactivity between the antigen and the monoclonal antibody and where the antigen has been fully characterized.  Later, this reasoning was applied to humanized antibodies and direct recognition of the significant advances in the field of antibody-related research led to a favourable result for the patentee.

Therefore, in Canada, a claim to an antibody specific for antigen X will be considered supported by a specification, even without CDR sequence(s) or evidence that such an antibody had been made as of the filing date, if antigen X itself has been fully characterized; and there no indication that would lead a person of skill in the art to question the likelihood of success if that person desired to produce such an antibody.

Of course, representative species and characterizing data are always desirable.  Further, test data such as that derived from epitope binning, alanine scanning, or similar tests can be used to characterize the function of representative antibodies species, elucidate possible structure-function relationships, thereby reducing the risk of invalidation based on insufficient written description and enablement.

While patentees must provide full and complete specifications, there is a danger in overly broad descriptions, which can also result in patent invalidity. The Supreme Court in AstraZeneca discusses the effect of descriptions that are overbroad. An overly broad description may be found to not fulfil the written description requirements of the Patent Act, and overpromising in a specification that is “willfully made for the purpose of misleading” may result in the entire patent being declared void. This is not validation of the so-called “promise doctrine” which had been used to measure utility against the promises in the specification, and resulted in entire patents being invalidated where a description promised a certain benefit, and the invention failed to provide that benefit. While the promise doctrine has been excised from Canadian law, drafters should still be cautious not to disclose or overstate advantages of an invention in the description that are unsubstantiated.

Further, the applicant must be cautious to provide a full and complete specification that still clearly and unambiguously discloses the invention. In Pfizer (the Viagra case) the patent application had claims including various compounds, only one of which was found to be effective or useful. Two compounds were specifically claimed, but nowhere in the application did it indicate that only one compound had been found to be effective. The Supreme Court concluded that because the skilled reader would have to conduct further testing in order to determine which compound was effective, that the patent application did not sufficiently disclose the invention.  This further testing was considered to go to the heart of the invention, and was therefore beyond routine experimentation.

It was decisive in the Supreme Court that Pfizer knew which compound was effective and chose not to disclose that information in the patent. Because the claims ended in two individually claimed compounds, only one of which was effective, the true invention was obscured. In this case because the application narrowed down to multiple claims, only one of which was useful, the public’s right to proper disclosure was denied and the patent was invalidated.

Thus, drafters of broad claims must ensure that the public can still discern the invention without the need for an individual skilled in the art to conduct testing. The Supreme Court confirmed that cascading claims starting broadly and narrowing down to the true inventive claim are permissible, as the skilled reader knows that useful claims are typically at the end of the cascade. However, a claim may be invalidated where it narrows down to multiple claims, some of which are not inventive, thereby obscuring the invention and not complying with public disclosure requirements. The presence of a single claim to the effective invention may not save the patent if other claims are presented as being equal, where the patentee knows otherwise. In such a case, because the patent is defective as a whole, all claims will be declared invalid.

Other Issues: Essential Elements, Background Information, and Consistory Clauses

When drafting a description to support broad claims, it is important that the essential elements of the invention disclosed in the description are also claimed.  If an essential element of the description is not claimed, then the patent may fail due to excessive breadth. The Aux Sable case is instructive – it involved an invention related to transporting natural gas by pipeline. The description of the patent noted that it is advantageous to add a gas that is ethane or propane in order to decrease the power needed to pump the mixture. The addition of ethane and propane was found to be an essential element of the invention, and therefore claims which did not include this element were found to be invalid.

Thus, where an invention has many alternate modes of operation, one should be especially cautious that one mode is not unintentionally described as an essential element of the invention.  If one mode of operation is found to be an essential element of the invention, then per Aux Sable, claims not involving that mode will be struck as overbroad.

Section 56(1)(c) of the Patent Rules requires a description of background art that is important for understanding the invention. Drafters should be cautious not too include too much information in the background, especially where identification of a problem is part of the invention. Because the background information is considered part of the common general knowledge of a person skilled in the art, the background information can be used to object to the patent based on obviousness. A broad specification does not necessarily need a broad background section.

It is common practice for descriptions to include consistory clauses, which mirror the language of the claims. In theory the consistory clause serves as a safeguard from a determination that the claims lack support in the description, or that the claims are broader than the invention described. However, many commentators disagree, as it is difficult to imagine how a description that otherwise does not support the claims could be found to be compliant simply by repeating the claim language. Mobil Oil is often cited for the proposition that mirroring the language of the claims in the description will not validate the patent (Mobil Oil was reversed on other grounds by the Federal Court of Appeal).


Like all aspects of patent law, the requirement for a full and complete description to support the entire scope of broad claims presents opportunities and pitfalls for patent practitioners.  We must steer between Scylla representing insufficient description, which could result in only narrow claims to specific examples being valid, while avoiding Charybdis representing a description which obscures the invention with overly broad or ambiguous statements, or which introduces unnecessary essentiality to some preferred embodiments.



Limitations of AI in Patent Searching

While AI has transformed various industries, its application in patent searching has limitations. Initial search results are often inaccurate, requiring human intervention to refine them. Additionally, AI tools often lack access to non-patent literature, posing a risk in comprehensive searches.

Read More

Get our insights delivered straight to your inbox.

Schedule a Demo

Schedule a Demo

Schedule a Demo

Schedule a Demo