Litigation for patent infringement arises when a party with the appropriate interest in a patent moves to accuse another party of using a patented invention in a manner contrary to the Patent Act without permission. When accused of patent infringement, defendants have the opportunity to argue that the patent asserted is invalid. As such, there can be no infringement as there is no patent. Typical invalidity attacks include lack of novelty (anticipation), prior use, prior publication, obviousness, inutility, insufficiency of specification, and non-patentable subject matter. Understanding this defence is crucial for both defendants seeking to protect their interests and patent holders seeking to enforce their rights effectively.
Prior Art - Prior art refers to any publicly available information or knowledge that existed before the earliest filing date of a patent application. It includes all relevant information that could affect patentability, including prior patents, scientific publications, public demonstrations, product manuals, or any other public uses and publicly accessible materials.
Person Skilled in the Art — The skilled person has been described as a legal creation that is deemed to have looked at and read publicly available documents and to know of public uses in the prior art, understand all languages and dialects, never miss the obvious or stumble on the inventive, have no private idiosyncratic preferences or dislikes, never think laterally, and brings to the workbench the common general knowledge and experience.
Typical Grounds for Invalidity
Lack of Novelty— Also referred to as anticipation, lack of novelty is a challenge to the validity of a patent on the basis that what is claimed is not new. This defense is typically raised when there exists a piece of prior art or a prior use that falls within the scope of the claims. The leading judgment on the question of lack of novelty/anticipation is Apotex Inc. v. Sanofi-Synthelabo Canada Inc.,  S.C.J. No. 63. Per Sanofi, the two requirements for anticipation are prior disclosure and enablement, namely, a prior disclosure that is sufficient for the skilled person to carry out the invention with ‘normal’ trial and error experimentation. Put another way, prior art or a prior use that would infringe the claim if later, anticipates the claim if earlier.
Prior Publication — Any document or publication that was generally available without restriction to the public prior to the earliest filing date and that discloses and enables the subject matter of the claim.
Prior Use— Flowing from lack of novelty, prior use can be alleged based on a sale, use or other demonstration by the inventor, or by use or knowledge disclosed by a third-party, prior to the earliest filing date. The test is analogous to lack of novelty with the additional exception for experimental use. The experimental use defence is available at common law and is also codified in subsection 55.3 (1) the Patent Act as “An act committed for the purpose of experimentation relating to the subject-matter of a patent is not an infringement of the patent”. Experimental use can apply to public use of the claimed invention, or even to non-commercial sales when deemed necessary to its development.
Obviousness — This is a common defense that challenges the validity of a patent on the basis that it was not inventive (as opposed to already known in anticipation). The test for obviousness (also from Sanofi) can be summarized as: identify the differences between the prior art and the inventive concept of the claim, and determine if those differences constitute steps which would have been obvious to the skilled person — which would render the claim non-inventive. This final step could also involve an “obvious to try” test, which considers a number of factors, including: whether or not a skilled person would find it self-evident that the invention would work, the effort required to come to the invention experimentally, and the motivation to find the solution based on prior art and the climate of the field of the invention. The series of questions aims to determine whether it was more or less self-evident for the skilled person to try to obtain the invention. However, an invention is not obvious where a series of choices and experimentation must be carried out to find the solution to a problem.
Inutility — The claimed invention must be useful. To determine if the claimed subject matter has utility, per AstraZeneca Canada Inc. v. Apotex Inc.,  S.C.J. No. 36, a court must first determine the subject-matter of the invention as claimed, and then ask whether that subject-matter is capable of a practical purpose. A scintilla of utility is sufficient. Moreover, as of the filing date of the patent application, the inventor(s) must have either demonstrated the claimed utility or been able to soundly predict the utility. That is, utility can be established by actual demonstration, such as a working embodiment of the claimed invention. If the utility was not demonstrated at the time of filing, it is sufficient if the inventor(s) could soundly predict the utility. The doctrine of sound prediction establishes the predictability of utility and requires a factual basis for the prediction (for example, experimental data), an articulable and sound line of reasoning, and proper disclosure. A complete theory of why the claimed invention would have the utility is not necessary and need not be disclosed in the patent.
Insufficiency of the Specification — As part of the “patent bargain” between the public and the patentee, the patent’s specification must correctly and fully describe the invention and its operation. A validity attack on the grounds of insufficiency alleges that the description is either lacking in sufficient detail such that a skilled person could not put the invention into practice (even using the common general knowledge), or that the specification does not adequately support the claims. For example, if the specification points to several solutions to a problem (e.g. pharmaceutical compounds) as being most preferred, but the evidence shows that only one of them works, then the disclosure may be insufficient.
Non-Patentable Subject Matter - An “invention” must be distinguished from a mere discovery, which is not patentable. Moreover, subsection 28(8) of the Patent Act provides two exception to patentability: “No patent shall be granted for any mere scientific principle or abstract theorem.” It is implicit in the definition of “invention” that patentable subject-matter must be something with a physical existence, or something that manifests a discernible change or effect. Human judgement and decision-making, artistic works, and subject matter that impinges on professional skills, such as methods of medical tyreatment, are also non-patentable subject matter.