a Canadian legal fiction used in patent law that is meant to denote someone of practical skill and knowledge in the subject matter of the patent, such as a technician. A Person Skilled in the Art is similar to the American standard of Person Having Ordinary Skill in the Art. A patented invention is thus separated into essential and non-essential elements. For an element to be classified as non-essential, it must be true that either: The words, interpreted purposively, make it clear that the element is not essential, or That, as of the date of publication, a person skilled in the art would have known of a substitute or variation that would not have affected how the invention works Any element that is not classified as non-essential is considered essential. It is important to note that if a patent is clear that an element is essential, then that element will be essential even if, at the time of publication of the patent, an element could be easily substituted or varied. Infringement It is an infringement to make, construct, or sell a thing that copies the essential elements of a patented invention without permission. Substitution or omission of a non-essential elements is not sufficient to make something non-infringing. The Canadian patent holder thus receives protection "against a device that performs substantially the same function in substantially the same way to obtain substantially the same result", similar to the protection available to an American patent holder under the doctrine of equivalents. Once the essential elements of the patented invention are established, determining whether there is an infringement is simply an exercise in comparison between the allegedly infringing thing and the patented invention. If the essential elements of the patented invention are present in the thing in issue, then that thing is infringing. In general, a defendant's intention is not relevant in establishing an infringement: the fact of infringement is sufficient. An exception arises in cases of infringement by possession. You can rebut a claim of infringement by possession by showing there was no intent to use or benefit from that possession. Using Cases alleging infringement based on "use" require special attention due to the difficulty in interpreting the term "use". Interpretation of the term "use" begins with the plain meaning of the words "use" and its French complement "exploiter". "Exploiter" was found to lend clarification to the term "use" in patent law,