Patent Specification Interpreted as Admission of Common General Knowledge

Patent Specification Interpreted as Admission of Common General Knowledge

Fiber optic cable photographed in the dark

Corning Cable Systems LLC v Canada (AG) (2019 FC 1065)

The specification of a patent application is often overshadowed by the claims, but a recent decision from Canada’s Federal Court reminds applicants of its importance. In its August 9th decision, the Federal Court used the specification to reject two patents from Corning Cable Systems LLC (“Corning”). The Federal Court cited a passage from both patent applications as being an admission of common general knowledge. In light of that knowledge, the patents were obvious and therefore ineligible for patent protection.


Canadian patent applications 2,679,996 and 2,754,149 were filed in 2008. They both claim improvements on Local Convergence Points (LCPs), which are devices adapted to distribute a single signal to multiple units in a building. An LCP receives a cable supplied by the internet service provider and splits it into smaller cables for individual units in a condominium, hotel, or office building.

Corning claims to have improved the LCP by using “bend performance optical fibers.” These fibers, which were previously known, can be bent to a smaller radius than traditional optical fibers. This allowed Corning to produce a smaller LCP that distributes fibers to more subscribers.

The Commissioner of Patents (“the Commissioner”) concluded that the use of bend performance optical fibers was obvious and therefore not patentable. Corning appealed that decision to the Federal Court. The question on appeal is whether the Commissioner erred in its application of the Sanofi test.

Sanofi Test for Obviousness

The Commissioner applied the Sanofi test in concluding that the patents were obvious. The Sanofi test asks what a skilled person in the relevant field would have known at the time and what is the innovative idea claimed in the patent application. If the differences between the skilled person’s common knowledge and the inventive idea would have been obvious at the time of invention, the application is denied.

What Was Known at the Time?

The Commissioner cited the background section of the patent as evidence that the problem Corning claims to have solved in its invention was obvious. The background section notes that “a need exists for LCPs that are cost-effective, are relatively small in size, and may be installed and maintained by relatively unskilled technicians.” [para 15] Corning argued that the background of the specification cannot be used as evidence of common general knowledge and that the Commissioner must cite external sources [para 51]. However, the Federal Court ruled that the Commissioner can consider a very broad range of sources, including the background section, when determining the state of the art (Also see Newco Tank Corp v Canada (AG)). [paras 55-56]

Was the Knowledge Gap Obvious?

Corning also argued that the Commissioner erred in determining that the gap between the common general knowledge and their proposed invention was obvious. Corning’s position was that, although the bend performance optical fibers were previously known, no one had disclosed how to use them in an LCP. [para 74] Developing the improved LCP box required testing and experimentation to optimize multiple factors, Corning alleged. [paras 76-77]

Once again, the Federal Court disagreed. In order to make a determination of obviousness, the Commissioner did not need to prove that every step of the proposed invention was already known. [para 87] Not only had bend performance optical fibers emerged in the industry, a Chinese patent published two years earlier had already suggested that their usefulness in optical devices. [para 83] The Court observed that “the very purpose for developing bend performance optical fibers appeared to be “miniaturization” of the optical splitter device.” [para 88] Therefore, the Commissioner was justified in finding that even an uninventive skilled person could have easily “bridged this gap.” [para 89]


While it is typical for applicants to acknowledge pre-existing patents and research papers in their specification, they may not expect the Commissioner to infer common general knowledge from their words. The passage in Corning’s patent that caused problems is one that every applicant typically includes: a statement of the problem that the invention purports to resolve. But it’s not clear whether a different wording would have saved Corning’s patents. On this point, the Federal Court noted that “a patent specification that sets forth a relatively unknown or obscure problem” would not likely be considered common general knowledge. [para 65] This ruling is in line with existing practices in the United States.

If you have any questions about patent drafting, please contact a professional at PCK Intellectual Property.