The Supreme Court of Canada has issued two new judgments on the interpretation of patent claims in Free World Trust v. Électro Santé Inc and Camco Inc v. Whirlpool Corporation. The decisions represent an interesting synthesis between the "purposive construction" to claim interpretation adopted in England in the Catnic decision of the House of Lords and the approach of the United States Supreme Court to equivalents in the Graver Tank case.

In the Free World Trust case, the main issue was whether the use of a "microcontroller" in the defendants dual action washing machine was an infringement of a claim that called for "control circuits" for the same purpose. The court started from the position that:

After likening a patent claim to a fence around a field that is protected, the Court went on to say:

Even if something did not fall within the literal wording of the claim, it could still be a "substantive infringement", if it included all of the essential features of the claim and there was variation only in the non-essential features. Thus the Court stated:

The court made it clear that what it meant by date of publication of a patent was the date of issue of a patent if it was issued under the former Canadian Patent Law under which applications were kept secret up to grant or the date of publication of a pending application if the application were filed under the present Patent Act. The Court also made it clear that it viewed the prosecution history of an application as being extrinsic evidence that should not be used to determine the meaning of a patent's claims, although the court did note that the prosecution history might be relevant for other purposes. Part of the test to be used in determining whether variants were possible was to consider whether at the time of publication it would have been obvious to a skilled reader that "substituting variants for the (element in question) would perform substantially the same function in substantially the same way to produce substantially the same result".

In construing the claim purposively, one should follow the guidance of the House of Lord's decision in Catnic. Once this was done the court concluded that the patentee had failed to show that at the time of publication one would not have regarded the control circuits as being essential so that replacement of them would result in something that was not a substantive infringement of the claim.

In Camco v. Whirlpool, the issue of claim construction arose in connection with a question of double patenting. The Court held this doctrine to be applicable in Canada, since the statute called for the grant of "a" patent for an invention and, ever since the reign of Henry VIII, the Crown had been precluded from granting two monopolies for the same thing at the same time. Both `same invention" and "obviousness-type" double patenting were recognized in Canada. The claim construction issue arose in that the patentee had brought suit on the later of two patents it owned that related to the subject matter in suit and the defendant claimed that this was invalid for obviousness type double patenting. This required consideration of the true scope of protection of the claims in the two patents. After establishing that Canadian case law had accepted the purposive construction approach of Catnic, the court went on to hold that the second patent which required "flex veins" in a dual action washing machine was invalid for obviousness type double patenting over the earlier patent which had not specified whether the veins were rigid or flexible.