Patents

Construction of Claims

John Lambert

1 March 2004
Last Updated 15 Nov 2005

It will be recalled that a patent is a monopoly granted by the state in exchange for disclosing an invention to the public. The document that discloses the invention and delineates the monopoly is called "the specification". S.14 (2) of the Patents Act 1977 requires the to be performed by a person skilled in the art. It also prescribes at least one claim that must be supported by the description which defines the matter for which protection is sought.

Applying the Protocols

The Court of Appeal considered the application of the Protocol on Interpretation in Wheatley v Drillsafe Ltd [2000] EWCA Civ 209 (5 July 2000) [2001] RPC 133 at paragraph [19]:

"The Protocol outlaws what can be termed strict literal and also liberal interpretation using the claims as a guideline. The correct approach is to achieve a position between those extremes 'which combines a fair protection for the patentee with a reasonable degree of certainty for third parties.' ”

He explained that although a strict literal interpretation using the drawings and specification gives to third parties the most certainty it is seen as unfair to patentees, which is why it is outlawed by the Protocol. So far as a patentee is concerned, it is important that a claim should be interpreted in accordance with his intention. A claim interpreted on the one hand too liberally can render the patent invalid and on the other too literally can allow third parties to avoid the monopoly. The object of interpretation is to ascertain the intention of the patentee.

The Improver Questions

To ascertain such intention, Hoffmann J (as he then was) suggested the following test in Improver Corporation v Remington Consumer Products Limited [1990] FSR 181:

”(1) Does the variant have a material effect upon the way the invention works? If yes, the variant is outside the claim. If no-
(2) Would this (i.e. that the variant had no material effect) have been obvious at the date of the publication of the patent to a reader skilled in the art. If no, the variant is outside the claim. If yes -
(3) Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention. If yes, the variant is outside the claim.
On the other hand, a negative answer to the last question would lead to the conclusion that the patentee was intending the word or phrase to have not a literal but a figurative meaning (the figure being a form of synecdoche or metonymy) denoting a class of things which included the variant and the literal meaning, the latter meaning, the latter being perhaps the most perfect, best-known or striking example of the class.”

The first 2 questions involve considerations of fact. The last is a question of construction. Aldous LJ explained at paragraph [25] of Wheatley that the first question envisages that the claim has an ambit wider than the literal meaning of the words so as to give fair protection for the patentee but that is subject to the safeguards contained in it when considered with the second. The third question also provides a fair result for the patentee in that it avoids an unintended meaning while requiring attention to the purpose of the words to give fair protection for third parties.
Contrast with the Doctrine of Equivalents

In the USA, a different rule of construction applies. In circumstances where all aids to interpretation have been exhausted and the scope of the claims has been enlarged as far as words can be stretched the courts may on proper occasions make them cover more than their meaning can bear (per Judge Learned Hand in Royal Typewriter v Remington (1948) 168 f. 2d. 691; 77 USPQ 517 (2d Cir.). This rule is balanced by a countervailing doctrine known as "file wrapper estoppel" which essentially means that a patentee may not go back on anything he has said or represented to the US Patent and Trademark Office when applying for a patent. The doctrine of equivalents and file wrapper estoppel have recently been reviewed by the US Supreme Court in Festo Corp. v Shoketsi KKK, and others 535 U.S. 722 (2002).  A case that illustrates the differences between the doctrine of equivalents and the Protocol is Celltech Chiroscience Ltd. v Medimmune Inc. [2003] EWCA Civ 1008, [2002] EWHC 2167 (Patents).

Revised Protocol
In Celltech, the trial judge remarked that prosecution history estoppel along with the doctrine of equivalents had become an elaborate doctrine with many facets which arise in most patent litigation in the USA. He observed "Those who suggest similar doctrines for Europe would do well to bear this in mind - and that the prosecution file may be in any of three languages." In fact, the doctrine of equivalents may well come to Europe because the Munich diplomatic conference voted for the following article to be added to the Protocol:

"For the purpose of determining the extent of protection conferred by a European patent, due account shall be taken of any element which is equivalent to an element specified in the claims."

This article will of, course, be incorporated by reference automatically into English law by s.125 of the Patents Act 1977. 

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