IP monitor - Derailed on obviousness: Court of Appeal reminds us the characteristics of the skilled worker and common general knowledge are key

Canada Publication August 2019

A case about inventions for railroads contains a powerful reminder: a patent is always directed to a defined audience, and the characteristics of that audience can dictate whether or not the patent is valid.

Why care about the skilled person? An introduction

Patents are drafted to be read by a “skilled worker” who would want to put the invention into use — not to the general public. The skilled worker is deemed to be uninventive, but possesses qualifications and characteristics that should — together with the specification of the patent — make it possible to put the invention into practice. Among those characteristics, the skilled worker is deemed to possess the common general knowledge in the relevant art. This knowledge and perspective is also brought to bear when interpreting the patent and considering the inventiveness of the claimed subject matter.

Thus, the qualifications, characteristics, and common general knowledge of the skilled worker can be central to the outcome of a patent dispute. It can mean the difference between whether or not the subject matter of the claims was obvious.

As the case of Tetra Tech EBA Inc. v Georgetown Rail Equipment Company illustrates, an obviousness analysis can quickly go off the rails if a court fails to tie its analysis back to the knowledge and perspective of the skilled worker or strays too far from the language of the claims when interpreting them.

Two patents valid and infringed in the Federal Court

In Tetra Tech, two patents-in-suit pertained to systems and methods using machine (as opposed to human) vision for: 1) inspecting railroad tracks; and 2) determining rail seat abrasions of a railroad track. 

In the Federal Court, the trial judge accepted that the common general knowledge  of the skilled worker to whom the patents-in-suit were directed would have included the application of machine vision techniques and an ancillary knowledge of railways. 

The defendant, Tetra Tech EBA Inc., argued the patents were invalid because the subject matter would have been obvious to the skilled worker. The trial judge rejected this argument, focussing on specific publications that Tetra had cited.

In the result, both patents were declared at trial to be valid and infringed by Tetra. 

Reversal by the Court of Appeal

The Federal Court of Appeal reversed the trial judge, finding the relevant claims of both patents to be invalid for obviousness. 

There are a few points of note from the Court of Appeal’s reasoning:

  • Laying the rails: the characteristics of the skilled worker. The Court of Appeal adopted the trial judge’s findings regarding characteristics of the skilled worker, including what constituted common general knowledge  of the skilled worker. 
    • In doing so, the Court of Appeal cautioned that “the identification of the ordinary person skilled in the art should be consistent with the specification of the patent.”
    • For the patents-in-suit, the Court of Appeal found that “the skilled worker has sufficient knowledge of railways and track inspection techniques to be able to apply machine vision techniques to rail inspection.”
  • Obviousness in the 082 Patent. With respect to Canadian Patent No. 2,572,082 (the 082 Patent), the Court of Appeal found that the trial judge committed an error of law by focusing on specific prior art publications without analysing how the skilled worker would, based on the common general knowledge, have responded to the problem addressed by the patent in light of that prior art.
    • Had the trial judge done this exercise, he would have found that the difference between the prior art and the claims of the 082 Patent could have been bridged by the skilled worker, applying only the common general knowledge. In other words: the 082 Patent was obvious and invalid.
    • There was nothing novel or inventive in using well-known technology (machine vision) to mimic a human inspector performing similar operations. It was therefore unnecessary to consider whether specific publications in the prior art disclosed either the problem to be solved, or the solution taught by the 082 Patent.
  • Obviousness in the 249 Patent.  With respect to Canadian Patent No. 2,766,249 (the 249 Patent), the Court of Appeal found that the trial judge erred in his construction of the three claims alleged to have been infringed. This led to a flawed obviousness analysis.
    • In construing the allegedly infringed claims, the trial judge gave too much attention to the patent disclosure and not enough attention to the words of the claims themselves. In doing so, he wrongly incorporated an additional essential element into these claims.
    • The Court of Appeal found that omitting the erroneous additional element, there was nothing inventive about the allegedly infringed claims over those of the 082 Patent. In other words: these claims of the 249 Patent were obvious and invalid.
    • At trial, Tetra also asserted that the remainder of the claims in the 249 Patent were invalid for obviousness (even though they were not infringed). The Court of Appeal was not prepared to make findings on the invalidity of the remaining claims because “[i]n addition to being fact driven, this was not an issue argued in sufficient detail before us.” The validity of the remaining claims of the 249 Patent was remitted to the trial judge.


As this judgment demonstrates, the Court of Appeal has recently shown itself  willing to review and modify the analysis of the trial judge on a range of substantive issues concerning patent interpretation and make highly factual findings concerning the validity analysis. 

Recent publications

Subscribe and stay up to date with the latest legal news, information and events...