(back to preceding text)

    32.  Construction, whether of a patent or any other document, is of course not directly concerned with what the author meant to say. There is no window into the mind of the patentee or the author of any other document. Construction is objective in the sense that it is concerned with what a reasonable person to whom the utterance was addressed would have understood the author to be using the words to mean. Notice, however, that it is not, as is sometimes said, "the meaning of the words the author used", but rather what the notional addressee would have understood the author to mean by using those words. The meaning of words is a matter of convention, governed by rules, which can be found in dictionaries and grammars. What the author would have been understood to mean by using those words is not simply a matter of rules. It is highly sensitive to the context of and background to the particular utterance. It depends not only upon the words the author has chosen but also upon the identity of the audience he is taken to have been addressing and the knowledge and assumptions which one attributes to that audience. I have discussed these questions at some length in Mannai Investment Co Ltd v Eagle Star Life Assurance Co Ltd [1997] AC 749 and Investors Compensation Scheme Ltd v West Bromwich Building Society [1998] 1 WLR 896.

    33.  In the case of a patent specification, the notional addressee is the person skilled in the art. He (or, I say once and for all, she) comes to a reading of the specification with common general knowledge of the art. And he reads the specification on the assumption that its purpose is to both to describe and to demarcate an invention - a practical idea which the patentee has had for a new product or process - and not to be a textbook in mathematics or chemistry or a shopping list of chemicals or hardware. It is this insight which lies at the heart of "purposive construction". If Lord Diplock did not invent the expression, he certainly gave it wide currency in the law. But there is, I think, a tendency to regard it as a vague description of some kind of divination which mysteriously penetrates beneath the language of the specification. Lord Diplock was in my opinion being much more specific and his intention was to point out that a person may be taken to mean something different when he uses words for one purpose from what he would be taken to mean if he was using them for another. The example in the Catnic case was the difference between what a person would reasonably be taken to mean by using the word "vertical" in a mathematical theorem and by using it in a claimed definition of a lintel for use in the building trade. The only point on which I would question the otherwise admirable summary of the law on infringement in the judgment of Jacob LJ in Rockwater Ltd v Technip France SA (unreported) [2004] EWCA Civ 381, at paragraph 41, is when he says in sub-paragraph (e) that to be "fair to the patentee" one must use "the widest purpose consistent with his teaching". This, as it seems to me, is to confuse the purpose of the utterance with what it would be understood to mean. The purpose of a patent specification, as I have said, is no more nor less than to communicate the idea of an invention. An appreciation of that purpose is part of the material which one uses to ascertain the meaning. But purpose and meaning are different. If, when speaking of the widest purpose, Jacob LJ meant the widest meaning, I would respectfully disagree. There is no presumption about the width of the claims. A patent may, for one reason or another, claim less than it teaches or enables.

    34.  "Purposive construction" does not mean that one is extending or going beyond the definition of the technical matter for which the patentee seeks protection in the claims. The question is always what the person skilled in the art would have understood the patentee to be using the language of the claim to mean. And for this purpose, the language he has chosen is usually of critical importance. The conventions of word meaning and syntax enable us to express our meanings with great accuracy and subtlety and the skilled man will ordinarily assume that the patentee has chosen his language accordingly. As a number of judges have pointed out, the specification is a unilateral document in words of the patentee's own choosing. Furthermore, the words will usually have been chosen upon skilled advice. The specification is not a document inter rusticos for which broad allowances must be made. On the other hand, it must be recognised that the patentee is trying to describe something which, at any rate in his opinion, is new; which has not existed before and of which there may be no generally accepted definition. There will be occasions upon which it will be obvious to the skilled man that the patentee must in some respect have departed from conventional use of language or included in his description of the invention some element which he did not mean to be essential. But one would not expect that to happen very often.

    35.  One of the reasons why it will be unusual for the notional skilled man to conclude, after construing the claim purposively in the context of the specification and drawings, that the patentee must nevertheless have meant something different from what he appears to have meant, is that there are necessarily gaps in our knowledge of the background which led him to express himself in that particular way. The courts of the United Kingdom, the Netherlands and Germany certainly discourage, if they do not actually prohibit, use of the patent office file in aid of construction. There are good reasons: the meaning of the patent should not change according to whether or not the person skilled in the art has access to the file and in any case life is too short for the limited assistance which it can provide. It is however frequently impossible to know without access, not merely to the file but to the private thoughts of the patentee and his advisors as well, what the reason was for some apparently inexplicable limitation in the extent of the monopoly claimed. One possible explanation is that it does not represent what the patentee really meant to say. But another is that he did mean it, for reasons of his own; such as wanting to avoid arguments with the examiners over enablement or prior art and have his patent granted as soon as possible. This feature of the practical life of a patent agent reduces the scope for a conclusion that the patentee could not have meant what the words appear to be saying. It has been suggested that in the absence of any explanation for a restriction in the extent of protection claimed, it should be presumed that there was some good reason between the patentee and the patent office. I do not think that it is sensible to have presumptions about what people must be taken to have meant but a conclusion that they have departed from conventional usage obviously needs some rational basis.

    36.  At the time when the rules about natural and ordinary meanings were more or less rigidly applied, the United Kingdom and American courts showed understandable anxiety about applying a construction which allowed someone to avoid infringement by making an "immaterial variation" in the invention as described in the claims. In England, this led to the development of a doctrine of infringement by use of the "pith and marrow" of the invention (a phrase invented by Lord Cairns in Clark v Adie (1877) 2 App Cas 315, 320) as opposed to a "textual infringement". The pith and marrow doctrine was always a bit vague ("necessary to prevent sharp practice" said Lord Reid in C Van Der Lely NV v Bamfords Ltd [1963] RPC 61, 77) and it was unclear whether the courts regarded it as a principle of construction or an extension of protection outside the claims.

    37.  In the United States, where a similar principle is called the "doctrine of equivalents", it is frankly acknowledged that it allows the patentee to extend his monopoly beyond the claims. In the leading case of Graver Tank & Manufacturing Co Inc v Linde Air Products Company 339 US 605, 607 (1950), Jackson J said that the American courts had recognised?

"that to permit imitation of a patented invention which does not copy every literal detail would be to convert the protection of the patent grant into a hollow and useless thing. Such a limitation would leave room for - indeed encourage - the unscrupulous copyist to make unimportant and insubstantial changes and substitutions in the patent which, though adding nothing, would be enough to take the copied matter outside the claim, and hence outside the reach of law."

    38.  In similar vein, Learned Hand J (a great patent lawyer) said that the purpose of the doctrine of equivalents was "to temper unsparing logic and prevent an infringer from stealing the benefit of the invention": Royal Typewriter Co v Remington Rand Inc (CA2nd Conn) 168 F2nd 691, 692. The effect of the doctrine is thus to extend protection to something outside the claims which performs substantially the same function in substantially the same way to obtain the same result.

    39.  However, once the monopoly had been allowed to escape from the terms of the claims, it is not easy to know where its limits should be drawn. In Warner-Jenkinson Co v Hilton Davis Chemical Co 520 US 17, 28-29 (1997) the United States Supreme Court expressed some anxiety that the doctrine of equivalents had "taken on a life of its own, unbounded by the patent claims." It seems to me, however, that once the doctrine is allowed to go beyond the claims, a life of its own is exactly what it is bound to have. The American courts have restricted the scope of the doctrine by what is called prosecution history or file wrapper estoppel, by which equivalence cannot be claimed for integers restricting the monopoly which have been included by amendment during the prosecution of the application in the patent office. The patentee is estopped against the world (who need not have known of or relied upon the amendment) from denying that he intended to surrender that part of the monopoly. File wrapper estoppel means that the true scope of patent protection often cannot be established without an expensive investigation of the patent office file. Furthermore, the difficulties involved in deciding exactly what part of the claim should be taken to have been withdrawn by an amendment drove the Federal Court of Appeals in Festo Corporation v Shoketsu Kinzoku Kogyo Kabushiki Co Ltd 234 F3rd 558 (2000) to declare that the law was arbitrary and unworkable. Lourie J said:

"The only settled expectation currently existing is the expectation that clever attorneys can argue infringement outside the scope of the claims all the way through this Court of Appeals."

    40.  In order to restore some certainty, the Court of Appeals laid down a rule that any amendment for reasons of patent validity was an absolute bar to any extension of the monopoly outside the literal meaning of the amended text. But the Supreme Court reversed this retreat to literalism on the ground that the cure was worse than the disease: see Festo Corporation v Shoketsu Kinzoku Kogyo Kabushiki Co Ltd (28 May 2002) US Supreme Court.

    41.  There is often discussion about whether we have a European doctrine of equivalents and, if not, whether we should. It seems to me that both the doctrine of equivalents in the United States and the pith and marrow doctrine in the United Kingdom were born of despair. The courts felt unable to escape from interpretations which "unsparing logic" appeared to require and which prevented them from according the patentee the full extent of the monopoly which the person skilled in the art would reasonably have thought he was claiming. The background was the tendency to literalism which then characterised the approach of the courts to the interpretation of documents generally and the fact that patents are likely to attract the skills of lawyers seeking to exploit literalism to find loopholes in the monopoly they create. (Similar skills are devoted to revenue statutes).

    42.  If literalism stands in the way of construing patent claims so as to give fair protection to the patentee, there are two things that you can do. One is to adhere to literalism in construing the claims and evolve a doctrine which supplements the claims by extending protection to equivalents. That is what the Americans have done. The other is to abandon literalism. That is what the House of Lords did in the Catnic case, where Lord Diplock said (at [1982] RPC 183, 242:

"Both parties to this appeal have tended to treat 'textual infringement' and infringement of the 'pith and marrow' of an invention as if they were separate causes of action, the existence of the former to be determined as a matter of construction only and of the latter upon some broader principle of colourable evasion. There is, in my view, no such dichotomy; there is but a single cause of action and to treat it otherwise…is liable to lead to confusion."

    43.  The solution, said Lord Diplock, was to adopt a principle of construction which actually gave effect to what the person skilled in the art would have understood the patentee to be claiming.

    44.  Since the Catnic case we have article 69 which, as it seems to me, firmly shuts the door on any doctrine which extends protection outside the claims. I cannot say that I am sorry because the Festo litigation suggests, with all respect to the courts of the United States, that American patent litigants pay dearly for results which are no more just or predictable than could be achieved by simply reading the claims.

    Is Catnic consistent with the Protocol?

    45.  In Improver Corp v Remington Consumer Products Ltd [1989] RPC 69 the Court of Appeal said that Lord Diplock's speech in Catnic advocated the same approach to construction as is required by the Protocol. (See also Southco Inc v Dzus Fastener Europe Ltd [1992] RPC 299.) But in PLG Research Ltd v Ardon International Ltd [1995] RPC 287, 309 Millett LJ said:

"Lord Diplock was expounding the common law approach to the construction of a patent. This has been replaced by the approach laid down by the Protocol. If the two approaches are the same, reference to Lord Diplock's formulation is unnecessary, while if they are different it is dangerous."

    46.  This echoes, perhaps consciously, the famous justification said to have been given by the Caliph Omar for burning the library of Alexandria: "If these writings of the Greeks agree with the Book of God, they are useless and need not be preserved: if they disagree, they are pernicious and ought to be destroyed" - a story which Gibbon dismissed as Christian propaganda. But I think that the Protocol can suffer no harm from a little explanation and I entirely agree with the masterly judgment of Aldous J in Assidoman Multipack Ltd v The Mead Corporation [1995] RPC 321, in which he explains why the Catnic approach accords with the Protocol.

    47.  The Protocol, as I have said, is a Protocol for the construction of article 69 and does not expressly lay down any principle for the construction of claims. It does say what principle should not be followed, namely the old English literalism, but otherwise it says only that one should not go outside the claims. It does however say that the object is to combine a fair protection for the patentee with a reasonable degree of certainty for third parties. How is this to be achieved? The claims must be construed in a way which attempts, so far as is possible in an imperfect world, not to disappoint the reasonable expectations of either side. What principle of interpretation would give fair protection to the patentee? Surely, a principle which would give him the full extent of the monopoly which the person skilled in the art would think he was intending to claim. And what principle would provide a reasonable degree of protection for third parties? Surely again, a principle which would not give the patentee more than the full extent of the monopoly which the person skilled in the art would think that he was intending to claim. Indeed, any other principle would also be unfair to the patentee, because it would unreasonably expose the patent to claims of invalidity on grounds of anticipation or insufficiency.

    48.  The Catnic principle of construction is therefore in my opinion precisely in accordance with the Protocol. It is intended to give the patentee the full extent, but not more than the full extent, of the monopoly which a reasonable person skilled in the art, reading the claims in context, would think he was intending to claim. Of course it is easy to say this and sometimes more difficult to apply it in practice, although the difficulty should not be exaggerated. The vast majority of patent specifications are perfectly clear about the extent of the monopoly they claim. Disputes over them never come to court. In borderline cases, however, it does happen that an interpretation which strikes one person as fair and reasonable will strike another as unfair to the patentee or unreasonable for third parties. That degree of uncertainty is inherent in any rule which involves the construction of any document. It afflicts the whole of the law of contract, to say nothing of legislation. In principle it is without remedy, although I shall consider in a moment whether uncertainty can be alleviated by guidelines or a "structured" approach to construction.

    49.  Although article 69 prevents equivalence from extending protection outside the claims, there is no reason why it cannot be an important part of the background of facts known to the skilled man which would affect what he understood the claims to mean. That is no more than common sense. It is also expressly provided by the new article 2 added to the Protocol by the Munich Act revising the EPC, dated 29 November 2000 (but which has not yet come into force):

"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."

    50.  In the Catnic case [1982] RPC 183, 243 Lord Diplock offered some observations on the relevance of equivalence to the question of construction:

"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.

The question, of course, does not arise where the variant would in fact have a material effect upon the way the invention worked. Nor does it arise unless at the date of publication of the specification it would be obvious to the informed reader that this was so. Where it is not obvious, in the light of then-existing knowledge, the reader is entitled to assume that the patentee thought at the time of the specification that he had good reason for limiting his monopoly so strictly and had intended to do so, even though subsequent work by him or others in the field of the invention might show the limitation to have been unnecessary. It is to be answered in the negative only when it would be apparent to any reader skilled in the art that a particular descriptive word or phrase used in a claim cannot have been intended by a patentee, who was also skilled in the art, to exclude minor variants which, to the knowledge of both him and the readers to whom the patent was addressed, could have no material effect upon the way in which the invention worked."

    51.  In Improver Corporation v Remington Consumer Products Ltd [1990] FSR 181, 189 I tried to summarise this guidance:

"If the issue was whether a feature embodied in an alleged infringement which fell outside the primary, literal or acontextual meaning of a descriptive word or phrase in the claim ("a variant") was nevertheless within its language as properly interpreted, the court should ask itself the following three 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 (ie 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.

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 include the variant and the literal meaning, the latter being perhaps the most perfect, best-known or striking example of the class."

    52.  These questions, which the Court of Appeal in Wheatly v Drillsafe Ltd [2001] RPC 133, 142 dubbed "the Protocol questions" have been used by English courts for the past fifteen years as a framework for deciding whether equivalents fall within the scope of the claims. On the whole, the judges appear to have been comfortable with the results, although some of the cases have exposed the limitations of the method. When speaking of the "Catnic principle" it is important to distinguish between, on the one hand, the principle of purposive construction which I have said gives effect to the requirements of the Protocol, and on the other hand, the guidelines for applying that principle to equivalents, which are encapsulated in the Protocol questions. The former is the bedrock of patent construction, universally applicable. The latter are only guidelines, more useful in some cases than in others. I am bound to say that the cases show a tendency for counsel to treat the Protocol questions as legal rules rather than guides which will in appropriate cases help to decide what the skilled man would have understood the patentee to mean. The limits to the value of the guidelines are perhaps most clearly illustrated by the present case and therefore, instead of discussing the principles in the abstract as I have been doing so far, I shall make my comments by reference to the facts of the case.

    53.  It will be recalled that claim 1 is to a DNA sequence, selected from the sequences set out in Table VI or related sequences, for securing the expression of EPO in a "host cell". The chief question of construction is whether the person skilled in the art would understand "host cell" to mean a cell which is host to the DNA sequence which coded for EPO. The alternative, put forward by Amgen, is that it can include a sequence which is endogenous to the cell, like the human EPO gene which expresses GA-EPO, as long as the cell is host to some exogenous DNA. In the TKT process, it is host to the control sequence and other machinery introduced by homologous recombination.

    54.  On this question, the judge had the advantage of hearing the evidence of a number of witnesses who were highly skilled in the art. They all said that they would have understood claim 1 to be referring to a DNA sequence coding for EPO which had been isolated or synthesised and was suitable for expression in a host cell. In other words, the claim was to a sequence coding for EPO which was exogenous to the cell in which expression took place. The judge summed up his conclusions in paragraph 215:

"I am of the view that a cell is not a 'host cell' unless it is host to exogenous DNA encoding for EPO or its analogue. Such a conclusion is based in part on the teaching of the [patent in suit]. The terms 'host' and 'host cell' are used consistently to describe cells which have been transfected with exogenous or foreign DNA (ie DNA from outside that particular cell) which encodes EPO, with a view to securing expression of EPO in those host cells. That was accepted by [Amgen's expert] Dr Brenner. The examples contained in the [patent in suit] are all concerned with EPO-encoding DNA which has been isolated outside the cell and inserted into the cell to which it is foreign. Indeed, at the relevant time, the routine method of production of a recombinant protein was by cloning the gene encoding the protein and the introduction of that clone into a self-replicating organism by transfection or transformation. There was no knowledge of the technique of 'switching on' an endogenous encoding sequence by transfecting the cell with exogenous DNA sequences as including an artificial promoter."

    55.  Besides these general considerations, the judge relied upon other indications in the language of the specification. The words "for use in securing expression … of a polypeptide" suggested the DNA which coded for that polypeptide rather than a control sequence which promoted expression of endogenous DNA. That was supported by paragraph (b) of claim 1, which extended the claim to sequences which were not in Table VI but which hybridised under stringent conditions to "the protein coding regions" of Table VI.

    56.  Furthermore, the specification appears anxious to point out that the invention covers the use of mammalian cells which already have an EPO gene of their own:

"It will be understood that expression of, eg, monkey origin DNA in monkey host cells in culture and human host cells in culture, actually constitute instances of 'exogenous' DNA expression inasmuch as the EPO DNA whose high level expression is sought would not have its origins in the genome of the host."

    57.  That certainly suggests that the patentee regarded it as essential to his invention that the DNA of which high level expression was sought should not have its origin in the genome of the host cell. That would clearly exclude the DNA sequence which expresses GA-EPO, which forms part of the genome of the host cell.

    58.  For these reasons, which I find entirely convincing, the judge came to the conclusion that the person skilled in the art would not regard the endogenous coding sequence which expressed GA-EPO as falling within claim 1. It followed that GA-EPO was not the expression of a DNA sequence within claim 1 and therefore did not infringe claim 26. And by the same process of reasoning, the judge concluded that the person skilled in the art would not regard GA-EPO as "the product of … expression of an exogenous DNA sequence" within claim 19. At this point in the judgment, TKT might have concluded that they had won. I shall return in a moment to consider why the judge nevertheless held claim 26 to have been infringed. But, first, I must dea1 with three criticisms of the judge's construction advanced by Mr Watson QC on behalf of Amgen.