the applicant must show that there is a sound factual basis for the invention and explain why the invention should work. This defence was successfully used in Minerals Separation North American Corp. v. Noranda Mines Ltd., where a mining company sued another for the use of a patented process using a xanthate frothing flotation method in order to separate minerals from ore. It failed because the patent claims included all xanthates, but it was known that not all xanthates could be used in the process. Consequently, the patent was held invalid as a person skilled in the art could not use the patent specifications in order to reproduce the effect and the patent was inoperable. However, in Burton Parsons Chemicals, Inc. v. Hewlett-Packard (Canada) Ltd., the same defence was not successful because a person skilled in the art would know which of the unspecified material could and could not be used. Anticipation An anticipation defence attempts to show that the invention was not new as of the claim date. The current test used in Canadian Patent law was enunciated in Apotex Inc. v. Sanofi‑Synthelabo Canada Inc. The test includes two prongs: prior disclosure and enablement. The prior disclosure requirement asks whether a person skilled in the art would know that the previous disclosure covered the same material as the patent at issue. There is no trial and error permitted at this stage of the inquiry - either doing what is specified in the earlier disclosure or patent would infringe the patent at issue, or it will not. The enablement requirement asks whether a person skilled in the art would be able to work the invention as disclosed in the prior art. Some experimentation is allowed at this stage of the inquiry, but the experimentation must not pose an undue burden. Long and arduous experimentation, for example, would indicate that the prior disclosure did not include enough information for a defence of anticipation to succeed. The earlier case Reeves Brothers Inc. v. Toronto Quilting & Embroidery Ltd. holds that the prior disclosure must include all requisite factors in a single document without making a mosaic. In Canadian patent law, there is a high bar for a test of anticipation to succeed. Obviousness An obviousness defence attempts to show that the invention is an obvious or logical next step of a previously disclosed invention. In order for the defence to succeed, it