have come directly and without difficulty to the solution taught by the patent. In Apotex Inc. v. Sanofi‑Synthelabo Canada Inc., Justice Rothstein adopted the approach from Windsurfing International Inc. v. Tabur Marine (Great Britain) Ltd.: Identify the notional “person skilled in the art” and identify the relevant common general knowledge of that person; Identify the inventive concept of the claim in question or if that cannot readily be done, construe it; Identify what, if any, differences exist between the matter cited as forming part of the “state of the art” and the inventive concept of the claim or the claim as construed; Viewed without any knowledge of the alleged invention as claimed, do those differences constitute steps which would have been obvious to the person skilled in the art or do they require any degree of invention? Each of these steps is crucial, and can affect the outcome of the obviousness inquiry. Cases can turn on the interpretation of who the presumed skilled person is, since this will affect how large a step is big enough for the subsequent invention to be considered non-obvious. A nuance to this test will be included for inventions in areas where advances are often won by experimentation; an “obvious to try” test can be used to extend obviousness and invalidate a patent. Commercial success of the invention sought to be patented also impacts a finding of obviousness. Obvious-to-try In fields where experimentation is common, such as in the pharmaceutical industry, an invention may be unpatentable if a skilled worker would have found it obvious to try the course that led to it. As stated by the Supreme Court of Canada in Apotex Inc. v. Sanofi‑Synthelabo Canada Inc., the following non-exclusive factors should be taken into consideration at the fourth step of the obviousness inquiry: Is it more or less self-evident that what is being tried ought to work? Are there a finite number of identified predictable solutions known to persons skilled in the art? What is the extent, nature and amount of effort required to achieve the invention? Are routine trials carried out or is the experimentation prolonged and arduous, such that the trials would not be considered routine? Is there a motive provided in the prior art to find the solution the patent addresses? If the answer to these questions leads to a finding that it was obvious to take this additional step,