Claim Ambiguity

The word ambiguity does not appear in the Patent Act. However, section 27(4) requires that a patent end with claims that distinctly and in explicit terms define the subject-matter of the invention. Simply put, a claim must be unambiguous.

(4) The specification must end with a claim or claims defining distinctly and in explicit terms the subject-matter of the invention for which an exclusive privilege or property is claimed.

Chief Justice Duff of the Supreme Court of Canada explained the effect of what is now subsection 27(4) of the Patent Act. He stated that the public is entitled to look at the claims in order to ascertain the limits of the monopoly granted to the patentee. These limits must be prescribed distinctly in the claims themselves, without unnecessary ambiguity, otherwise the claims are unenforceable.

But there is something more to be said about the effect of clause (c) in the subsection of the Patent Act [now subsection 27(4) of the Patent Act] quoted above. To use Lord Halsbury’s language, that clause requires that the ambit of the invention must be circumscribed by a claim or claims at the end of the specification. It is to these claims that the public are entitled to look in order to ascertain the limits of the monopoly granted to the patentee, and unless these limits are prescribed distinctly in the claims themselves, without unnecessary ambiguity, vagueness or obscurity, having regard to the nature of the subject-matter, the patentee can found no title to relief upon his patent in respect of any alleged infringement …

President Thorson expressed the requirement for unambiguous claims in terms of fences. An inventor uses claims to fence off the fields of his or her monopoly. The fences allow the public to know where it will trespass and where it may safely go. A claim is ambiguous if the public does not know where it must not trespass or where it may safely go.

By his claims the inventor puts fences around the fields of his monopoly and warns the public against trespassing on his property. His fences must be clearly placed in order to give the necessary warning and must not fence in any property that is not his own. The terms of a claim must be free from avoidable ambiguity or obscurity and must not be flexible; they must be clear and precise so that the public will be able to know not only where it must not trespass but also where it may safely go. If a claim does not satisfy these requirements it cannot stand. [p. 352]

In Free World Trust, Justice Binnie emphasized the purpose and importance of requiring clear language in the drafting of patent claims. He stated that the scope of claims must be made clear so that members of the public may know where they can go with impunity.

14 Patent claims are frequently analogized to fences and boundaries, giving the fields of the monopoly a comfortable pretence of bright line demarcation. Thus, in Minerals Separation North American Corp. v. Noranda Mines, Ltd., [1947] Ex. C.R. 306, Thorson P. put the matter as follows, at p. 352:

By his claims the inventor puts fences around the fields of his monopoly and warns the public against trespassing on his property. His fences must be clearly placed in order to give the necessary warning and he must not fence in any property that is not his own. The terms of a claim must be free from avoidable ambiguity or obscurity and must not be flexible; they must be clear and precise so that the public will be able to know not only where it must not trespass but also where it may safely go.

15 In reality, the fences often consist of complex layers of definitions of different elements (or components or features or integers) of differing complexity, substitutability and ingenuity. A matrix of descriptive words and phrases defines the monopoly, warns the public and ensnares the infringer. In some instances, the precise elements of the fence may be crucial or essential to the working of the invention as claimed; in others the inventor may contemplate, and the reader skilled in the art appreciate, that variants could easily be used or substituted without making any material difference to the working of the invention. The interpretative task of the court in claims construction is to separate the one from the other, to distinguish the essential from the inessential, and to give to the field framed by the former the legal protection to which the holder of a valid patent is entitled.

…

41 The scope of patent protection must not only be fair, it must be reasonably predictable. A patent is, after all, a public instrument issued under statutory authority which may result in severe financial consequences for its infringement. The scope of its prohibition should be made clear so that members of the public may know where they can go with impunity. As was said in another public law connection by Gonthier J. in R. v. Nova Scotia Pharmaceutical Society, [1992] 2 S.C.R. 606, at p. 639, precision in public enactments is required to sufficiently delineate an area of risk.

42 The patent system is designed to advance research and development and to encourage broader economic activity. Achievement of these objectives is undermined however if competitors fear to tread in the vicinity of the patent because its scope lacks a reasonable measure of precision and certainty. A patent of uncertain scope becomes a public nuisance (R.C.A. Photophone, Ld. v. Gaumont-British Picture Corp. (1936), 53 R.P.C. 167 (Eng. C.A.), at p. 195). Potential competitors are deterred from working in areas that are not in fact covered by the patent even though costly and protracted litigation (which in the case of patent disputes can be very costly and protracted indeed) might confirm that what the competitors propose to do is entirely lawful. Potential investment is lost or otherwise directed. Competition is chilled. The patent owner is getting more of a monopoly than the public bargained for. There is a high economic cost attached to uncertainty and it is the proper policy of patent law to keep it to a minimum.

In Minerals Separation UKPC, a decision of the Privy Council affirming the Supreme Court of Canada, a claim using the phrase alkaline xanthate was found to be ambiguous and invalid. The claim in question read as follows:

6. The process of concentrating ores which consists in agitating a suitable pulp of an ore with a mineral-frothing agent and an alkaline xanthate adapted to co-operate with the mineral frothing agent to produce by the action of both a mineral-bearing froth containing a large proportion of a mineral of the ore, said agitation being so conducted as to form such a froth, and separating the froth. [Emphasis added.]

However, there is no such thing as an alkaline xanthate. Lord Reid noted that even if a person skilled in the art would realize that a mistake had been made, a claim cannot be valid unless it is clear from the evidence that a person skilled in the art would have no doubt about what was meant.

[A person skilled in the art of froth flotation] would then discover, if he did not know it already, that there is no such thing as an alkaline xanthate: all xanthates are neutral and none is alkaline. If the matter rested there the claim would clearly be valueless. As all xanthates are neutral he could work with any of them without infringing the claim. But the appellants seek to save the claim by arguing that he would at once realise that the patentee had made a slip of the pen and would at once see what was meant. No doubt he would at once realise that a mistake had been made because it cannot be supposed that a patentee would deliberately use a meaningless expression or make a claim which is valueless. But, even if it be assumed that this mistake could be treated as a mere clerical error, the claim cannot be valid unless it is clear from the evidence that persons to whom the specification is addressed would have no doubt about what was meant. The law as to ambiguity is clear and their Lordships need only refer to a well known passage in the speech of Lord Loreburn in Natural Colour Kinematograph Co. Ltd. v. Bioschemes Ltd. (1915) 32 R.P.C. 256, where he says

It is the duty of a patentee to state clearly and distinctly, either in direct words or by clear and distinct reference, the nature and limits of what he claims. It he uses language which, when fairly read, is avoidably obscure or ambiguous, the Patent is invalid, whether the defect be due to design, or to carelessness or to want of skill. Where the invention is difficult to explain, due allowance will, of course, be made for any resulting difficulty in the language. But nothing can excuse the use of ambiguous language when simple language can easily be employed, and the only safe way is for the patentee to do his best to be clear and intelligible.

[p. 5]

The alleged mistake was that by the phrase an alkaline xanthate the patentee meant an alkali metal xanthate. However, Lord Reid determined that the phrase could reasonably have a different meaning — it could mean a xanthate used in an alkaline circuit. The test for evaluating whether the claim was ambiguous was: If a metallurgist wished to use in an alkaline circuit a xanthate of a metal other than an alkali metal, would it be obvious to him that this was not an infringement of Claim 6? The answer was no, and therefore the claim was ambiguous and invalid.

The appellants’ case is that the instructed reader would at once see that when the Patentee said alkaline xanthate he meant alkali metal xanthate. The term alkali metal is well known: it means anyone of five metals, sodium, potassium and three rarer metals, which chemists class together. The appellants get support from their expert Mr. Higgins but the other expert witnesses do not agree and Thorson P. did not find in favour of the appellants on this question. Before coming to claim 6 the instructed reader would have observed in claim 5 the phrase an alkali-metal salt of an ethyl-sulphur derivative of carbonic acid. So he would see that the patentee was well able to use the term alkali metal when that was what he meant, and he would naturally assume that when the patentee used another word he intended a different meaning. So if the word alkaline in claim 6 could reasonably have a different meaning he could not safely assume that it was a mistake for alkali metal. At least one other meaning is suggested by the respondents’ witnesses. The process of froth flotation was found by metallurgists to work best in some circumstances when the pulp had been made alkaline and in other circumstances when it had been made acid or neutral. Metallurgists speak of an alkaline circuit, an acid circuit, or a neutral circuit. So it would not be unreasonable to suppose that an alkaline xanthate meant a xanthate used in an alkaline circuit. The matter may be tested in this way. If a metallurgist wished to use in an alkaline circuit a xanthate of a metal other than an alkali metal would it be obvious to him that this was not an infringement of claim 6? In their Lordships’ judgment it would not, and this claim is ambiguous and invalid.

[pp. 5-6]

A claim is not ambiguous and invalid simply because it is capable of more than one construction or because it is difficult to construe.

12 With reference to the contention that, in so far as they relate to softening temperatures, the product claims are ambiguous with the result that the claims are invalid as not complying with section 36(2) of the Patent Act, while the claims in question are difficult to construe, it does not follow, in my view, that, when construed, they do not comply with section 36(2). On this point, I rely on the reasoning of Lord Reid in Henrickson v. Tallon Limited, where he said: [Footnotes omitted.]

It remains to consider the question of ambiguity. That word is not used in the statute. The ground of invalidity in section 32(1)(i) of the Act is that the scope of the claim is not sufficiently and clearly defined. The authority generally referred to on this matter is the speech of Lord Loreburn in Natural Colour Kinematograph Co. v. Bioschemes (1915) 32 R.P.C. 256. Having animadverted on the practice of deliberately trying at the same time to make the claim wide and to insert carefully prepared limitations, he said: If he (the patentee) uses language which, when fairly read, is avoidably obscure or ambiguous, the patent is invalid, whether the defect be due to design, or to carelessness or to want of skill. I know of no authority for applying this ground of invalidity merely because some part of a claim is capable of more than one construction. Even the most careful draftsman of any kind of written instrument sometimes uses phrases capable of more than one construction, and it would in my view be applying the wrong standard to hold that this claim is ambiguous in this sense merely because part of it is difficult to construe.

The Federal Court of Appeal reviewed the jurisprudence on ambiguity and emphasized that in determining ambiguity, rather than only considering that which warns of the use of ambiguous language in a patent claim, a judge must also consider various other principles of patent law.

One of the principles of patent law that should be considered is that where the language of the specification, upon a reasonable view of it, can be so read as to afford the inventor protection for that which he has actually in good faith invented, the Court will endeavour to give effect to that construction.

32 In the present case it is contended that the phrase a distributing agent is vague and ambiguous because it refers to a substance that improves distribution of a softener in a clothes dryer and produces very superior results but does not say how it does so. That the trial judge had no difficulty in interpreting the term in the light of the whole of the specification and the evidence adduced is clear from the passage I have recited from page 31 his reasons for judgment. To him the meaning of distributing agent was crystal clear and not ambiguous. I agree with counsel for the respondents that the trial judge came to the correct conclusion on the point. In Consolboard, supra, Dickson, J., referred to Western Electric Co. v. Baldwin International Radio, [1934] S.C.R. 570, where Duff, C.J.C., stated at page 574:

[T]he courts, as in the case of other documents, have, where they have been satisfied that there was a meritorious invention, resorted to the maxim ut res magis valeat quam pereat. And, where the language of the specification, upon a reasonable view of it, can be so read as to afford the inventor protection for that which he has actually in good faith invented, the court, as a rule, will endeavour to give effect to that construction.

This too is an important principle of patent law; it was applied by this court in Computalog, supra, at page 84.

33 In my view, the correctness of the trial judge’s decision on the point should be tested against all of the foregoing principles rather than only against that which warns of the use of ambiguous language in a patent claim. When that is done, as I am satisfied was done by the trial judge, it will be seen that no error was committed in finding the phrase a distributing agent unambiguous.

Mobil Oil is illustrative of a claim that was found to be clear. The claim, reproduced below, related to a method of manufacturing a metallized film intended for use as a packaging material for snack foods, such as potato chips. It was alleged that the claim was avoidably ambiguous in that there was no clear indication as to which of two layers (either a polypropylene layer or a copolymer layer) was being referred to by the expression said layer in its wording.

15. A method for producing a metal coated oriented polypropylene substrate comprising

coextruding a homopolymer polypropylene layer which is from about 80% to 100% isotactic and has a melt index of from about 2 to about 10 grams/10 minutes with an ethylene propylene copolymer layer on at least one side of said polypropylene layer, said copolymer containing from about 2% to 4% by weight of ethylene and from about 96% to about 98% by weight of propylene, said layer containing either no slip agent or no slip agent which adversely affects the adhesion of the substrate to a metallized coating;

biaxially orienting said film substrate; subjecting at least one copolymer surface to corona discharge treatment to enhance adhesion of a metallized coating thereto; and

applying a metallized coating to the corona discharge treated surface, said metallized coating being of a metal selected from the group consisting of aluminium, copper, silver and chromium.

[Emphasis added.]

The trial judge held that, even though the only reasonable interpretation possible was that said layer referred to the copolymer layer, the phrase was ambiguous given the diverse opinions of the experts.

[21] The trial judge held that the phrase said layer in claim 15 was avoidably ambiguous, at least from the point of view of the experts who gave evidence at the trial. He wrote (at p. 21 of the reasons): Given the diverse opinions of the experts with respect to this phrase and the insufficiency of the disclosure to illuminate the meaning, the patent cannot be maintained as valid. Yet, in the course of construing the patent, the judge, as mentioned above, had come to the conclusion that the phrase necessarily referred to the copolymer bonding layer, as that was the only reasonable interpretation possible, when the claim is read as a whole. And he was, in my view, quite right in that respect. …

However, the Federal Court of Appeal stressed that a judge is the final interpreter of the language of the claim, and the judge’s interpretation cannot be outweighed by a conflict in the interpretations provided by experts. The Court added that it could not see how a phrase which can be interpreted using grammatical rules and common sense can be found to be ambiguous. Since it was logical that said layer referred to the copolymer layer, the claim was not ambiguous.

[21] … The phrase said layer immediately follows a description of the copolymer layer. Looking at the structure of the sentence, said layer must refer to the copolymer layer. Furthermore, claim 15 teaches that the slip agent must not adversely affect bonding of the metal to the substrate. Given that the metal is applied to the copolymer layer, it is only logical that this is the meaning of said layer.

[22] I simply do not see how a phrase which can be interpreted using grammatical rules and common sense can be found to be ambiguous. The trial judge relied on the fact that the experts appeared to adopt different ways of reading the text and, as a result, provided conflicting interpretations of the phrase. So, the learned trial judge permitted the conflict among the experts to outweigh his own interpretation and, moreover, a common sense interpretation. With respect, I think that was an error. The expertise of the witnesses had nothing to do with grammatical and linguistic difficulties and no doubt common sense was not their exclusive prerogative. In any event, as recalled above, it is a well settled principle that, while a judge may seek the assistance of experts in construing a patent, he should never forget that he is the final interpreter of the language.

According to Justice Hughes, there is a temptation to throws up one’s hands and say that a claim is not capable of any, or any one, construction.

[49] There is a temptation, particularly in hotly contested cases, to throw up one’s hands and say that the claim is not capable of any construction, or any one construction. That is, it is ambiguous, therefore, invalid.

However, in reviewing the jurisprudence on ambiguity, he observed that Canadian courts have resisted holding claims to be incapable of meaning and that ambiguity is rarely to be used to invalidate a patent.

[53] In short, ambiguity is truly a last resort, rarely, if ever, to be used.

See Minerals Separation UKPC above.

In Xerox, claims that used the words substantially tangential were held to be ambiguous and invalid:

The major issue on the construction of claims 2, 4, 5, 12 and 14 was as to the meaning, if any, to be given to substantially tangential, substantially tangentially and tangential. Those are the words used in those claims. …

Mr. Becker and Mr. Noto testified that to them substantially tangential included any angle of developer flow to the drum less than 45° down to zero. Zero degrees was, for the purposes of this discussion, assumed to be true tangent. …

I have, as required, tried to put myself in the role of a skilled addressee. When I read the patent as a whole, and keeping in mind the employment in it of tangential, alone and with differing adverbs, I conclude the claims must be declared invalid because of obscurity or ambiguity. I am not persuaded the skilled addressee of this patent would conclude that substantially tangential meant some angle of flow between zero and 45°. Nor am I persuaded that the patentee has made reasonably clear to that addressee the sacrosanct territory.

I have reluctantly come to this conclusion. I am convinced there was inventive ingenuity in this method. I am convinced also there was more than a mere scintilla of invention.

The fault, as I see it, is with the drafter of the specification. One must allow for deficiences in drafting. In these claims they are, however, fatal.

[Footnote omitted; pp. 82-83]

In Hoffmann, the claim language effective in the treatment of SMX-resistant bacterial infections was found to be ambiguous.

Claim 1 of the patent is a claim for the combination itself, modified by the words effective in the treatment of SMX-resistant bacterial infections. This wording, as it seems to me, can be read in at least two ways. One may read the words as limiting the scope of the claim to the combination when and only when it is effective in the treatment of SMX-resistant bacterial infections. In that event, as it was and is known that the combination was useful in the treatment of sulphona-mide-sensitive bacterial infections, it would be impossible for anyone to know, at least in advance, when a manufacture or use or sale of the combination would be within the claim. The answer would lie only in the ultimate use of the combination against SMX-resistant bacteria and whether it had been effective. Another interpretation is that the wording says such a combination is effective against SMX-resistant bacteria but does nothing to restrict the claim to the combination when made or sold or used for that purpose. In this interpretation, the claim is one for the combination per se, however made or sold or used. The claim is thus ambiguous and in either case it is invalid as well, in the first as not being sufficiently explicit to inform the reader as to what is within and what is not within the claim, as required by subsection 36(2) of the Patent Act, in the second in claiming more than the new use the inventor discovered for the known combination.

The Federal Court summarized Hoffmann this way:

[135] In Hoffman, supra, the questioned phrase was effective in the treatment of smx-resistant bacterial infections. I think it is irrelevant that it was in a combination claim. The Court of Appeal found that the phrase could be read in at least two ways. One could read the words as limiting the scope of the claim to the combination when and only when it was effective in treating such infections. If read in that manner, it would be impossible to know whether use of the combination would infringe the claim until its effectiveness had been demonstrated. Alternatively, the phrase says that such a combination is effective for treating infections but does not restrict the claim to the combination when made or sold for that purpose. Thus it was held to be ambiguous and invalid for not being sufficiently explicit to inform the reader of what was within or not within the claim.

According to Pollard, a claim that cannot be given any reasonable interpretation is ambiguous. Moreover, a dependent claim is ambiguous if it includes a limitation that is incompatible with the elements of a claim from which it depends.

[143] In my view, claim 2 cannot be given any reasonable interpretation because the additional limitation of claim 2 is incompatible with the elements of claim 1 which are incorporated into claim 2 by its dependency.

(3) Conclusion on Ambiguity

[144] The allegation of invalidity of claim 1 for ambiguity fails. However, claim 2 is invalid for ambiguity.