Retrospective - Interpretation of Patent Claims

Patents can be, and more often than not, are incredibly complex and technical. In such complexity accuracy is paramount, especially to guarantee proper protection for the rights you wish to protect. When a patent is applied for the person or entity registering the patent has to specify the claims relating to the patent, or in other words, what the person or entity endeavors to protect with their patent. The wording used when writing claims will create the remit in which protection is awarded for that patent. As such the claims of patents are hugely important, and should things get to litigation, what the wording used protects can be equally, or even more important than what is thought it protects. How these claims are interpreted therefore needs to be expanded on, and the United Kingdom House of Lords did so in the 1980s.

A modern use of angles

The decision in question is Catnic Components Ltd v Hill & Smith Ltd. The case concerned the production of steel lintels, which the plaintiff owned the patent for and manufactured. The lintels had a very specific rear support member, which under one of their claims was described as a "...second rigid support member extending vertically from or from near the rear edge of the first horizontal plate or part adjacent its rear edge". The defendant in question made a similar lintel, but one where the rear support member had an inclination between 6 to 8 degrees; something which deviated only that much from the plaintiff's vertical rear support member. This affected the load-bearing capabilities of the lintels, making the defendant's lintels approximately 0,6 to 1,2 percent weaker than the plaintiff's lintels. The plaintiff sued the defendant for patent infringement, ultimately ending up in the House of Lords.

Due to the slight deviation of the defendant's lintels' construction, the House of Lords had to decide whether this would still infringe the patent owned by the plaintiff. In more simple terms: whether the claim described above could be interpreted as such to include a slight deviation, or whether its express term of verticality would prevent the defendant from infringing the patent. This would have to be assessed based on the 'pith and marrow' of the claim; something which the Lords would have to consider in their judgment. What this encompasses was expressed well by Lord Diplock: "...a patent specification is a unilateral statement by the patentee, in words of his own choosing, addressed to those likely to have a practical interest in the subject matter of his invention (i.e. "skilled in the art"), by which he informs them what he claims to be the essential features of the new product or process for which the letters patent grant him a monopoly". How one would interpret claims based on their 'pith and marrow' was finally expressed by his Lordship:

"A patent specification should be given a purposive construction rather than a purely literal one derived from applying to it the kind of meticulous verbal analysis in which lawyers are too often tempted by their training to indulge. The question in each case is: whether persons with practical knowledge and experience of the kind of work in which the invention was intended to be used, would understand that strict compliance with a particular descriptive word or phrase appearing in a claim was intended by the patentee to be an essential requirement of the invention so that any variant would fall outside the monopoly claimed, even though it could have no material effect upon the way the invention worked."

This would indicate that patent claims should not purely be interpreted literally, but given a more of a purpose based assessment. Under this one could easily include slight deviations in the use of patented inventions, should the deviation still be within the purpose of the patent. A much larger change could clearly not fall under a claim, even under a purpose based assessment.

Under their Lordships' deliberation, the defendant had infringed the plaintiff's patent. Even though their construction was different, the claim was thought to have included these small variants. Clearly their Lordships intended to not limit the scope in which patent claims would be interpreted as being all too literal, and allowed for potential differences to still be included. Should strict compliance be an essential part of the patent, for more technical or functional reasons, one would have to interpret the claim more literally.

Even though the case pertained to the old Patents Act 1949, it is still accepted to apply to the current Patents Act 1977 equally. Lord Diplock's reasoning has also been utilized in several other common law countries; making the decision an important one even in today's patent litigation.