Kirin-Amgen Inc v Transkaryotic Therapies Inc (No.2)¹, the long-awaited case in which the applicability of a purposive approach to construction of patent claims was considered in light of the Patents Act 1977 and the EPC, turns ten this month and, in light of this distinction, Lord Hoffmann was invited to address the IPSoc on the topic of “Kirin-Amgen: 10 years on”. Kirin-Amgen was, of course, the case in which Lord Hoffmann affirmed Lord’s Diplock’s position in Catnic Components Ltd v Hill & Smith Ltd (No.1)², that “A patent specification should be given a purposive construction rather than a purely literal one”, giving the language of the claim the meaning which would have been understood by the “notional addressee” - the person skilled in the art. It is a memorable decision for its direct and simplified approach to the construction of claims and, arguably, one of Hoffmann’s most significant contributions to the field of patent law.

Lord Hoffmann began by attributing his interest in the legal concept of construction of documents to a profound interest in language, how it is used and how we ought to interpret it.

Understood in context, he said, the traditional English legal approach to construction of documents came from the need to deal with two distinct problems. The first of these was that, until the beginning on the 19th century, many jurors were illiterate and therefore a necessary fiction was created - that the construction of documents was a legal question that went to judges who decided on law rather that the jury who, of course, decided on facts. The second problem was the more general need in the legal sphere to have uniform construction of commercial documents.

Lord Hoffmann highlighted the legal transition to today from the middle of the 19th century, where only the words of the document could be construed without judges having recourse to the surrounding facts, stressing the fact that the Chancery Division applied the same attitude to the construction of claims in patents. By the 20th century there was a general shift towards looking at the surrounding circumstances (permitted where there was ‘ambiguity’ in the wording) which was, according to Hoffmann, sometimes a result of judges ‘inventing’ ambiguities to bring these surrounding circumstances in.

For patents of course, the major change in the court’s approach to construction came with the Catnic decision (under the Patents Act 1944) and Lord Diplock’s purposive approach to construction of patent claims; the question being whether a person skilled in the art would understand that strict compliance with the words in the 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 had no material bearing on the functioning of the invention. Lord Diplock clarified that the question would not arise where the variant did have a material effect on the way the invention worked or if, at the date the specification was published, it would have been obvious to the informed reader that the variant would have a material effect.

While Lord Hoffmann praised this innovation, he was critical about taking such a rigid approach to the construction of documents. He was even more critical about his own approach in Improver Corporation and Others v. Remington Consumer Products Limited and Others³ which resulted in the three ‘Protocol’ questions:

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 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.

This approach, he stated, was too prescriptive because it was impossible to impose structure on questions of interpretation. If you do, he argued, you will find that judges make up their minds regardless of what the questions are and, only once they have made up their mind on whether the claim is infringed, will they then go through the process of mechanically answering the questions to fit their predetermined judgment. He contrasted the Improver approach with the approach taken in later decisions relating to the construction of commercial documents, such as his own judgment in Investors Compensation Scheme LTD. v West Bromwich Building Society and Others⁴ in which Lord Hoffmann held that the meaning of a document should be interpreted as by a reasonable person having all the background knowledge which would reasonably have been available to the parties, excluding pre-contractual negotiations and declarations of subjective intent. He strongly resisted the idea that the application of such an approach applies “plaster and bandages” to badly drawn agreements, but emphasised that language has to be interpreted in light of its context and its intended audience (of particular importance to patent lawyers with their concepts of a person skilled in the art).

The general message conveyed, and which Lord Hoffmann said he wanted to convey in Kirin-Amgen, was that language is subtle and, like twisting a kaleidoscope, a single shift in context can change in the entire picture. “Language is uncertain,” he mused, “No, that is unfair – language can be uncertain. And when it is there are no rules which can cure its uncertainty.”

Since Kirin-Amgen, the Improver questions have all but disappeared, although Hoffmann noted their recent mention by Arnold J in Actavis UK Limited v. Eli Lilly and Co.⁵. He said that this was “reminiscent” of Improver because of the similar attitudes of the German courts which he thought still, despite the guidance in the Protocol on the Interpretation of the European Patent Convention Art.69, seemed to prefer their traditional approach of protecting the spirit of the patented invention rather than sticking to the language of the claims.

Hoffmann was also struck by Arnold J’s treatment of the prosecution history in Actavis. In that case Arnold J stated that, while he accepted the courts should be cautious before relying upon prosecution history as an aid to construction, there were cases where the prosecution history clearly shows why claims were expressed in a particular way in the granted patent. In such circumstances, Arnold J stated that “there is no good reason why the court should shut its eyes to the story told by the prosecution file.” He considered Actavis itself to be such a case. As the claims had been narrowed at the EPO it would not be appropriate to construe them in accordance with the broad form of claims prior to the EPO’s examination. Lord Hoffmann admitted that, in patent cases, he may have been more influenced by the commercial rule that pre-contractual negotiations are not admissible in order to interpret the meaning of a document than he ought to have been.

Lord Hoffmann finished by surmising that the English approach to construction of claims is that it is considered a fair reward for the patentee that he or she should get what the person skilled in the art would think he is claiming, in line with the requirements of the Protocol on Art.69. He also emphasised the very distinct difference in legal culture between the English and German approaches, not only to construction of patent claims, but also to patent claims generally, with particular reference to the bifurcation of validity and infringement proceedings which exists in Germany. Whilst he acknowledged the existence of arguments in favour of such a system, Lord Hoffmann hinted that the advantages of bifurcation were more practical than principled. Having one branch of the court considering validity and another considering infringement at different times can have very different consequences, unlike in the UK where the proceedings deal with both issues together. It remains to be seen, he said, how the two distinct approaches will operate against a changing European context and especially in light of the development of the Unified Patent Court.