Principles of Claim Construction

1Patents should be interpreted purposefully, balancing the fair protection for the patentee with a reasonable degree of certainty for third parties. The canons of construction offer guidance in interpreting a patent and an over-rigid application of any of them may not be appropriate. (Brugger v Medic-Aid Ltd (1996) RPC 635, pp 641-42.) The general principles applicable for the construction of patents have been comprehensively discussed in Glaverbel SA v British Coal Corpn, a decision granted under the UK Patents Act 1949, where Staughton LJ summarised the following principles: ((1995) RPC 255, pp 268-270, [1995] FSR 254, pp 263-265. See also Osram Lamp Works Ltd v Pope's Electric Light Co Ltd (1917) 34 RPC 369; British Celanese Ltd v Courtaulds Ltd (1935) 52 RPC 171 (HL); Electrical & Musical Industries Ltd v Lissen Ltd (1938) 56 RPC 23; General Tire & Rubber Co v The Firestone Tyre and Rubber Co Ltd (1972) RPC 457; Strix Ltd v Otter Controls Ltd [1991] FSR 354.)

(1) The interpretation of a patent, as of any other written document, is a question of law. That does not mean that the answer to it will necessarily be found in our law books. It means that it is for the judge rather than a jury to decide, and that evidence of what the patent means is not admissible. In particular, evidence of the patentee as to what he intended it to mean should not be admitted, nor indirect evidence which is said to point to his intention. Compare the rule that the parties to a deed or contract cannot give evidence of what they intended it to mean. A patent is construed objectively, through the eyes of a skilled addressee.

(2) The court may, and indeed should, have regard to the surrounding circumstances as they existed at the date of the publication of the specification (or perhaps the priority date). Those circumstances, sometimes described as 'the matrix' in a commercial context, would include common general knowledge. I imagine that they would not include circumstances known only to the patentee or a limited class of persons, since every skilled addressee should be able to know what the patent means and therefore have equal access to material available for interpretation.

(3) The court should admit evidence of the meaning of technical terms. It may be that expert evidence can go somewhat further than that in aid of interpretation; but I need not decide that in the present case.

(4) The whole document must be read together, the body of the specification with the claims. But if a claim is expressed in clear language, the monopoly sought by the patentee cannot be extended or cut down by reference to the rest of the specification.

(5) The court must adopt: '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' Catnic Components Ltd v Hill & Smith Ltd [1982] RPC 183 by Lord Diplock, p 243.

This has become a popular theme in recent times, for the interpretation of contracts and statutes. But what does it mean? There is a clear contrast with meticulous verbal analysis, or the 'narrowly semantic approach' (also described by Lord Diplock, in Fothergill v Monarch Airlines Ltd [1981] AC 251 at p 280). If possible, the meaning of the document must be moulded to conform with the purpose of its author or authors—the purpose being judged from the document as a whole and the surrounding circumstances.

To put it another way, there is a conflict with the purpose if a judge is disposed to say to himself—'he cannot have meant that'. In the Catnic case itself, Lord Diplock said (at p 244): 'No plausible reason has been advanced why any rational patentee should want to place so narrow a limitation on his invention. On the contrary, to do so would render his monopoly for practical purposes worthless…'

That is in my view an example of the purposive method of construction. It is at least allied to, and perhaps an example of, what Lord Reid said in L Schuler AG v Wickman Machine Tool Sales Ltd (1974) AC 235, 251: 'The fact that a particular construction leads to a very unreasonable result must be a relevant consideration. The more unreasonable the result the more unlikely it is that the parties can have intended it, and if they do intend it the more necessary it is that they should make their intention abundantly clear.'

(6) Subsequent conduct is not available as an aid to interpretation of a written document. That too was established by the Schuler case, re-affirming an earlier decision of the House of Lords.

(7) A claim must not be construed with an eye on prior material, in order to avoid its effect: Molins Ltd v Industrial Machinery Co Ltd (1938) 55 RPC 31, 39.

2A patent specification contains both technical as well as legal information about an invention. While the technical aspects 'describe' the invention, the legal aspects 'demarcate' the invention." (See Kirin-Amgen Inc v Hoechst Marion Roussel Ltd (2005) RPC 9, [2005] 1 All ER 667, para 33.) The construction of patents involves a unique situation where the language of science is tested by the language of law. It entails an exercise of giving meaning to the words used by the patentee judged from the standard of a person skilled in the art. As a legal document, it contains a unilateral expression of intention of the inventor. Courts have reiterated the legal nature of a patent specification by stipulating that it should be constructed like any other legal document, in accordance with the recognised cannons of construction, and not by their strict literal meaning. (See Electric and Musical Industries Ltd v Lissen Ltd [1938] 4 All ER 221, p 224, (1939) 56 RPC 23, p 39 (HL), per Lord Russell of Killowen.) Despite their special nature, patents are predominantly legal documents and its construction is for the court alone. (Catnic Components Ltd v Hill & Smith Ltd (1982) RPC 183, p 243, [1981] FSR 60 (HL) per Lord Diplock.) (Kirin-Amgen Inc v Hoechst Marion Roussel Ltd (2005) RPC 9, [2005] 1 All ER 667, paras 27-32.) (Lubrizol Corpn v Esso Petroleum Co Ltd (1998) RPC 727, p 738.)

3The phrase 'person skilled in the art' is not defined under the Patents Act, though it is mentioned in s 2(1)(ja) in the context of determining obviousness. The person skilled in the art is also known as a notional skilled addressee to whom the patent is deemed to have been addressed. As a hypothetical construct, the addressee is taken to be an unimaginative person who lacks inventive capacity but at the same time is deemed to have common general knowledge of the subject matter of the invention. A patent is supposed to teach people how to perform the invention. If necessary information is not present in the patent, then the skilled person must be given a clear unambiguous direction on where to get it. He cannot be expected to find such a direction buried in acknowledgements of the prior art. (Halliburton Energy Services Inc v Smith International (North Sea) Ltd [2006] EWCA Civ 1715, para 67 (CA).)

Document to be read as a whole

4One of the foundational principles of claim construction is the principles that patent specification and the claims should be read as a whole. In Cipla v F Hoffmann-La Roche (2015) (paras 67 and 94) the Division Bench summarised the principles of claim construction and held, "It is a cardinal principle of claim construction that the claim must be interpreted on its own language and if it is clear then resort cannot be had to subsequent statements or documents either to enlarge its scope or to narrow the same." In Farbwerke Hoechst v Unichem Laboratories (1968) (p 60) the Bombay High Court held that "The claims must, however, be read as ordinary English sentences without incorporating into them extracts from the body of the specification, or changing their meaning by reference to the language used in body of the specification" and that "in an infringement action the main function of the court is to construe the claims which are alleged to have been infringed, without reference to the body of the specification, and to refer to the body of the specification only if there is any ambiguity or difficulty in the construction of the claims in question". The Court's observation that the claims need to be construed without reference to the body of the specification may not be in line with the principles that have evolved subsequently.

5In Merck Sharp and Dohme v Glenmark Pharmaceuticals (2015) (para 56) the Division Bench held that "A patent is construed by reference to the words used by the inventor, and not her subjective intent as to what was meant to be covered".