Chapters 4 & 5:
Claim Construction & Infringement

copyright 1996 - 1999 Donald M. Cameron, Aird & Berlis

Cameron's Canadian Patent & Trade Secrets Law:Home Page; Index
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A Precise Test for Claim Construction

by Donald M. Cameron

"It is a long time since I have attended a gathering of the scientific world - a world in which I am at home - one in which men deal with realities and where truth is, in fact, the goal. For the past ten years I have been in exile from this world and an explorer in another - a world where men substitute words for realities and then talk about the words. Truth in that world seems merely to be the avowed object. Now I undertook to reconcile the objects of these two worlds and for a time I believed that could be accomplished. Perhaps I still believe it - or perhaps it is all a dream."

Edwin Howard Armstrong, inventor of regeneration and FM radio, in an address to the annual convention of the Institute of Radio Engineers, Philadelphia, U.S.A., May 29, 1934.(1)


When a patent is written, the invention is described in the disclosure of the patent in words and figures and in the claims in words alone. In litigation, those words are then construed and compared to the prior art to determine the validity of the patent and to the defendant’s device or process to determine infringement.

In theory, reading a patent and giving it meaning should not be a difficult exercise. However, most patent infringement and validity cases turn on the question of claim construction and the determination of the scope of the claims of the patent.

Canadian Courts are repeating claim construction tenets from past cases like a mantra spoken in a foreign language, and construing claims in a consistently bizarre pattern that bears no resemblance to consistent, predictable jurisprudence.

As a result, the outcome of patent infringement cases are as predictable as lotteries; with winners an losers shaking heir heads at the process.

The time has come for reform, either initiated by the Court or by Parliament.

This paper suggests a new way to interpret the claim language of patents, that draws from the best parts of earlier tests and abandons a rewriting of the claim while allowing for equitable flexibility to provide a fair interpretation for both patentee and alleged infringers. This paper first examines the nature of a patent claim as well as the development of the current methods of claim construction, criticizes the test created in the Catnic case and sets out a new alternative that is consistent with most of the guiding principles of claim construction.

Scientific Verity

Before we look at what Mr. Armstrong described as "a world where men substitute words for reality and then talk about the words", we should first examine Armstrong's world of science and engineering, where people "deal with realities and where truth is, in fact, the goal." Until it is understood what scientists and engineers are dealing with, our words describing their reality will not do the job adequately.

Firstly, science is not nature; science is our description of nature. It is sometimes only an approximate description. Dr. Richard Feynman, a brilliant physicist and one of its best teachers conceded that

"...we do not yet know all the basic laws: there is an expanding frontier of ignorance... Each piece, or part, of the whole of nature is always merely an approximation to the complete truth, or the complete truth so far as we know it. In fact, everything we know is only some kind of approximation, because we know that we do not know all the laws as yet. Therefore, things must be learned only to be unlearned again or, more likely, to be corrected.

The principle of science, the definition, almost, is the following: The test of all knowledge is experiment. Experiment is the sole judge of scientific "truth." But what is the source of knowledge? Where do the laws that are to be tested come from? Experiment, itself, helps to produce these laws, in the sense that it gives us hints. But also needed is imagination to create from these hints the great generalizations--to guess at the wonderful, simple, but very strange patterns beneath them all, and then to experiment to check again whether we have made the right guess."

It is the recognition of patterns in nature that allow scientist to create the so-called "laws" of nature. These are in fact laws of humans, and are subject to being overthrown by the "more correct" laws of nature themselves through experimentation..

So whether scientists use words or mathematical formulae to describe natural "laws", these "laws" all are approximations, imperfect abstractions based on our imperfect observations and incomplete understanding.

In using numbers to describe scientific phenomenon, scientists have recognized this uncertainty in the way that they express the observed quantity. If there are 52 grams measured in one sample and 55 grams measured in a second sample, the total would be expressed as 110 grams plus or minus 5 grams because there are only two "significant digits" in the initial samples. A scientist would read this as meaning the total is somewhere between 105 and 115 grams, but the inherent errors in the measurements do not give us a clearer idea of the exact value of the total.

Numbers are rounded upwards from the half below and downwards up to the half above. For example something having a value of 6 could be any value between 5.5 and 6.49. On the other hand when scientists describe something as having a weight of 6.002 grams, they mean that it is between 6.0015 and 6.00249. Thus the number of significant digits expressed is an indication of the precision of the value - the specificity of the description.

Precision and Accuracy

For the purposes of this paper, I will use terms "precision" and "accuracy" as they are commonly used by engineers:

"Precision" defines the error, scatter or degree of uncertainty surrounding a fact

"Accuracy" is a measure of correctness or "truth".

We deal with precision and accuracy in our everyday lives.

Something can be precise without being accurate. Our quartz wrist watches can tell us the time within seconds and can maintain that precision for months or years but are only accurate if we calibrate them by setting them according to "the correct time". Our bathroom scales are precise to within two pounds (the gradations on the scale) but are not necessarily accurate (Compare the measurement at home with that at the doctor's office!).

In the bulls eye shown below, the grouping of the holes is an indication of the precision that was achieved by the shooter. The holes are generally grouped close together showing good precision, but are offset from the bullseye a noticeable distance to the right, showing less than perfect accuracy.

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Likewise, we can have accuracy with varying degrees of precision. All of these answers to the question "How old are you?" are accurate, depending upon the degree of precision wanted by the questioner:

What is Claim Construction?

A patent claim is a single sentence describing the invention as claimed by the inventor(s). The inventor creates an idea and a way of carrying it out: an embodiment of the invention. The patent claim is a higher-level functional or generic description of the embodiment of the invention. The claim is not meant to protect a specific embodiment of the invention - instead, it is meant to protect the invention incorporated in the embodiment. The claim should contain the minimum number of words necessary to protect the invention - anything more is unnecessary verbiage.

How then showed a court construe a patent? Should it:

Currently, the Canadian Courts do both, or either depending upon the judge and the particular facts of the case.

The Canadian Courts are using two mutually inconsistent tests:

• one of strict construction where the words of the claim are limited to their plain meaning and none can be ignored or altered;

• the other, amending the language of the claim to broaden its scope beyond that of the strict language (referred to in the decisions as infringement of the "pith and substance" or infringement by the "doctrine of equivalents", referred to in this paper as "equitable infringement").

All the while, Canadian judges and their English counterparts state that they are consistently applying only one rule of construction: a purposive construction.

The use of these two very different tests results in unpredictable and inconsistent results and uncertainty and dissatisfaction amongst litigants.

The Patent Claim

Section 27(4) of the Patent Act(2) requires the patentee to end the patent with the claims:

"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."

Interestingly, the statutory requirement that patent end with claims was introduced to the Canadian Patent Act by 1923 (s.14, The Patent Act, S.C. 1923, c.23).

The patent's claims define the monopoly in words. The ambit of the invention must be circumscribed by definite claims.(3) A patent may have many claims, each defining the invention in different words and describing it broad or narrow functional language.

In Canada, claims are most commonly of the form having a brief preamble describing the apparatus or method in terms of its field of use, the transition "comprising"(3a) , and followed by the claim elements (apparatus elements or process steps) which are like a checklist of the components of the claimed invention. Crudely speaking, if an potential infringer's device or process has each and every element listed in a claim, then there is infringement of that claim.

Claims are sometimes analogized as a series of "fences" surrounding and protecting the valuable invention. The claims define the metes and bounds surrounding the protected invention, much like surveying terminology defines the metes and bounds to a piece of land containing gold. The fences must be clearly defined in order to give the necessary warning. Property which is not owned by the inventor must not be fenced in, otherwise the claim will be invalid as being broader than the invention.(4)

Claims are usually drafted with multiple, dependant claims. As such, they are like a set of nested fences, each fence surrounding a more particularized form of the invention. If one of the outer most fences fails because it is invalid, the inner ones remain to protect the invention. The larger fences are the broad claims; the narrowest fences are the narrow claims.

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Another way of considering a claim is to describe them by use of a Venn diagram, a mathematical illustration used to identify "sets". The Venn diagram of some claims would be analogous to an aerial photograph of the "fences" surrounding the invention. The claims would be a series of sets and subsets, all including the invention at the centre of the sets. Anything that met the description of that set, would fall inside that claim and infringe it.

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The invention can be described in a number of ways and therefore, there can be different sets of claims each with dependant claims, all protecting the invention at the core.

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Claim Drafting

While it is beyond the scope of this paper to explain how one drafts a patent claim, the intention of the patent drafter must be appreciated so that its general rules of construction can be appreciated.

Because the claim is supposed to protect the functionality of the invention and not be limited to the specific "nuts and bolts" that inventor may have built, the patent drafter attempts to create a "higher level" description of the invention, extracting only what is essential to the operation of the invention. Thus an inventor should only claim what is considered to be essential to the use of the invention.

In this respect, the role of the patent drafter is much like that of a scientist trying to create a general theory as to how the device or process works. If the inventor has designed or built one of a species, the patent drafter attempts to claim the genus or family.


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For example, if the inventor has produced a device that has two parts ("members") held together by nuts and bolts, the patent drafter (with the aid of cross-examining the inventor as to what is needed and what is not) would soon appreciate that the same function could be served by a rivet or by a nail. The patent drafter might combine these particular devices into a more generic descriptor, such as "fasteners" or "fastening means", or better still might recognize that the members need only be connected (by fasteners or by being molded together as an integral piece) and thus might settle on language such as "the first member being connected to the second member" without narrowing the claim to be limited to devices held together by fasteners. This would include all manners of nuts an bolts, rivets, nails and other fasteners or even members that are integrally connected (ie. unitary construction). By describing the invention in higher and higher levels of functional abstraction, the claim (and the resulting protection) becomes broader. The patent drafter should also include claims citing specific hardware elements in case the broader claims are later found to be too broad as encompassing later revealed prior art

The choice of the wording used to describe the invention is that of the inventor (or, more accurately, the patent drafter). The inventor may be as cautious and as bold as he or she desires, but once the language of the claims is finalized during the prosecution of the application, they cannot be changed (subject to reissuance or reexamination procedures).

Because the claim is a checklist, the patent drafter tries to use as few words as possible: the greater the number of words, the easier it will be for someone to avoid infringement by eliminating claimed elements.

The Role of the Court in Claim Construction

There a some general rules of claim construction that appear to have survived even the most illogical of decisions. They are set out below.

The First Duty

The first duty of the Court is to construe the claims alleged to be infringed(5) to give them meaning and to determine the scope of the claims.(6) This is to be done before issues or infringement(7) or validity(8) are determined so that a consistent reading of the patent is applied to questions of infringement and validity.

A Question of Law

Claim construction is a question of law.(9) A Canadian patent trial judge hears all the evidence at trial and determines construction after hearing final argument making the ruling in the Reasons for Judgment.

Because many U.S. patent trials are decided by judges and juries, American patent trials since 1996 have held Markman hearings (named after the case when the practice began(10)). Before the trial by jury begins, the judge hears evidence and construes the patent. The jury then deals with the issues of fact such as infringement.

Pre construction "set up"

The judge must put him or herself in the proper mindset to read the patent:

(1) expertise

The patent should be read and understood from the viewpoint of the addressee of the patent: a skilled worker in the field of the invention of the patent.(11) In some cases, the addressee may be a team of people having different expertise.(12) Only those familiar with the field of the invention can be expected to make anything of the claims.(13) The knowledge that such a person is expected to possess is to be taken into account.(14) The question to be asked by the Court is: How would a workman in the trade understand it?(15)

The claims are to be interpreted by applying the common vocabulary of the art.(16) For example: if a claim used the word "bolt", what would that term mean in the context of that patent? Depending upon the art to which the patent is directed, it could mean a threaded screw to be used in conjunction with a nut as a fastener, an 8 foot length of a tree trunk or a length of cloth wrapped around a cardboard spindle. It is language as generally understood, not that defined by an obscure reference.

Although the interpretation of the claims is a matter for the Court, the Judge may be assisted by the evidence of an expert who is knowledgeable in the field to which the claim is directed. Such evidence may relate to the state of the art at the date of the patent, the meaning of technical terms and the working of the invention.(17) In the past, an expert witness was not entitled to state what the specifications meant nor whether any given step or alteration was obvious.(18) This has given way to the current practice of expert witness giving opinion on virtually every issue, including infringement or validity, and the Judge applying whatever weight should be given to such evidence.(19)

(2) interpretation as of what date

Although the debate continues as to the effective date on which a patent is to be interpreted (the date of the filing of the first application, or the date of issuance of the patent), current authorities state that a patent is to be construed as at the date it issued.(20) This factor is only relevant if the meaning of the words used in the patent have changed over time.

(3) attitude of the reader (Court)

The patent should be read by a mind willing to understand, not a mind desirous of misunderstanding. It ought not to be construed malevolently, but need not be construed benevolently.(21) It must be fairly and reasonably construed, being fair to both the patentee and the public.(22) The patent should be read to afford protection to what has been invented.(23) A patent should be approached with a judicial anxiety to support a really useful invention. One should not be too astute or technical in raising objections to the specifications.(24)

(5) objectiveness

Some cases say that the construction of the claim is to be done without having in mind the alleged infringement(25) or as one judge described it, "as if the defendant had never been born" (Judge Ford, UK Patents County Court).

Although objectivity is a laudable principle, in fact there is usually only a word or phrase or two in the entire claim that is at issue in the lawsuit and it makes sense that the Court need only focus on that part of the claim at issue when it construes the language. Although the structure of the defendant's allegedly infringing device is irrelevant to issues of construction, the Court must at least be aware of what elements of the claim is alleged by the defendant not to be present in the defendant's device.

Construing the patent

It has been said that the Court should construe a patent just as it would construe any other document such as a written contract.(26)

The process by which patents are issued suggests that the concept of contra preferentem be borrowed from the principles of contract interpretation: the terms of the contract will be interpreted against the person who drafted it. Thus if an inventor decides to include a certain element in his or her claim, and patentees are supposed to only claim what is essential to the working of their invention, why should the Court ignore that element in construing that claim?(27)

Step #1 The patent should be read as a whole

The document should be construed (and read) as a whole.(28) During the reading, the disclosure should be examined for definitions which state the meaning of words used in the patent. Such definitions apply to the words used in the claims, thereby defining their scope.(29) Unless a term has been defined in the dictionary sense in the disclosure, or by reference to a publicly available document,(30) a word or phrase should be given its ordinary meaning.(31) The words should be given a natural and not a strained meaning.(32)

Rule #1: Don't make reference to the disclosure unless the words in the claim are ambiguous

Reference may be made to the disclosure "... in order to understand what the former says" but only where the words of the claim are ambiguous. Reference to the disclosure is improper to vary the scope or ambit of the claims.(33)

The specification is not the dictionary by which the scope and effect of the terms of the claim is to be ascertained, in particular where the claim is expressed in simple and direct language or in wide or general terms whose meaning is plain and unequivocal.(34)

Rule #2 The disclosure cannot vary the scope or ambit of the claims if the language of the claim is plain and unambiguous.

A patentee cannot use general language in the claim and subsequently restrict or expand it to qualify what is expressed in the claim by borrowing from other parts of the patent.(35)

You cannot diminish the ambit of the monopoly claimed merely because in the disclosure, the patentee has described the invention in more restricted terms than in the claim itself.(36) The invalidity of a claim cannot be avoided by attempting to narrow the scope of a claim based on language used in the disclosure. To do so would be like throwing scientific dust in the eyes of the Court.(37) The reason for this is that patent drafters might make the claim very wide upon one interpretation, in order to prevent as many people as possible from competing with the patentee's business, and then try to rely on carefully prepared sentences within the disclosure to limit the claim so as to be valid.(38)

Fox suggested that variations described in the disclosure may have the effect of widening the scope of the claims by showing that there may a substitution of means.(39)

The claims are not limited to the specific examples or embodiments described in the patent.(40) The Court cannot limit the claims by simply saying that the inventor must have meant to claim what he had described in the disclosure. If the claims are broader than the disclosure and go beyond the invention, the patent will be declared invalid.(41)

If the disclosure states in the "Summary of the invention" section that there are certain "objects" to the invention, you cannot read those objects into a claim when interpreting the claim.(42)

Use of external material to interpret a patent

Parole evidence is admissible to explain the meanings of words or technical matters and to inform the Court of relevant surrounding circumstances.(43)

Notes made by an inventor are not relevant in construing the claims,(44) nor is the testimony of the inventor.(45) The inventor is not the best witness to claim construction. The inventor will have a strong self-interest and may not be reading the claim as an objective and first-time reader.(46)

The patent should not be limited in scope by prior art.(47)

use of the file wrapper

The "file wrapper" is the name given to the file in the Patent Office containing the correspondence between the inventor's patent agent and the patent office examiner during the prosecution of the patent. It sometimes contains statements made on behalf of the inventor as to what is the invention or how it differs from the prior art.

The Canadian or foreign patent application file relating to the patented issue cannot be admitted into evidence in Canada to limit the construction put on the claims.(48)

The file wrappers have been ruled inadmissible when they relate to changes made during the application(49) or to stop a party from denying that certain elements were "essential elements" to a claim (Amfac at p. 86-87).(50)

The absolute exclusion of the admissibility of file wrappers may be weakening (See AlliedSignal trial reasons at p. 31)

claim differentiation

Each claim is to be construed and given a distinct meaning. Differently worded claims are to be interpreted differently.

Strict vs. Equitable Construction

The Courts of "Law" (as compared to the Courts of Equity) limited the relief they would grant. In the case of contractual relief, parties were often required to comply with the strict wording of their agreement. On the other hand, the Courts of Equity would strive to do what was fair in the circumstances, even if it required departing from the strict wording of a contract.

This split personality is evident in the strict construction and equitable construction techniques described below.

Strict Construction

If the words of the claim, upon a plain reading of them, aptly describe the defendant's device or process, then there is said to be "literal infringement". This result seems self evident and straightforward - so much so that very few cases are litigated all the way to trial because the outcome is so predictable.

Under strict construction of a claim, all elements are considered to be essential to the invention). The absence of any claimed element, under the method of strict construction results in a finding of non-infringement.

One of the earliest, and oft cited case is Electric and Musical Industries, Ltd. et al v. Lissen, Ltd. et al(51) where Lord Russell of Killowen held at p. 39:

"The function of the claims is to define clearly and with precision the monopoly claimed, so that others may know the exact boundaries of the area within which they will be trespassers. Their primary object is to limit and not to extend the monopoly. What is not claimed is disclaimed. The claims must undoubtedly be read as part of the entire document, and not as a separate document; but the forbidden field must be found in the language of the claims and not elsewhere. It is not permissible, in my opinion, by reference to some language used in the earlier part of the specification to change a claim which by its own language is a claim for one subject-matter into a claim for another and a different subject-matter, which is what you do when you alter the boundaries of the forbidden territory. A patentee who describes an invention in the body of a specification obtains no monopoly unless it is claimed in the claims. As Lord Cairns said, there is no such thing as infringement of the equity of a patent (Dudgeon v. Thomson, L.R. 3 App. Cas. 34)."

The most recent example of strict construction from the highest authority (the Federal Court of Appeal) was O'Hara Manufacturing Ltd. et al v. Eli Lilly & Co. et al (52)

The patent claim related to a device for coating tablets that resembled a coin-operated clothes drier. As shown in the patent drawing, Figure 2 below, the tablets tumbled as a bed 17. Air was drawn through the bed of tablets by means of a vacuum system drawing air through plenum 21 that road on wheels 25 along the foraminous (provided with holes) outer surface of the drum. Because the drum 11 was not perfectly circular, the plenum was pressed against the drum to have its wheels ride against it, or in the words of the claim, the plenum was "flexibly biased against the drum" by piston 34 and levers 32 and 29.

Thomas Engineering, Eli Lilly's licensee, learned to make the drum more truly circular and did away with the piston and lever arm, fixedly securing the plenum on the frame so that it was spaced slightly away from the drum, touching it only with a resilient (flexible?) skirt. O'Hara copied the improved commercialized design without the piston arrangement.

At p. 5

"According to that theory, a court in deciding whether there is infringement, must first interpret the claims and determine whether there is textual infringement, and if it does not find textual infringement, it must engage in the difficult process of distilling the claims and extracting the substance of the invention so as to determine whether the defendant did steal it."

At. p. 5-6

"... the patentee is tied strictly to the invention which he claims and the mode of efffecting an improvement which he says is his invention."

The Court of Appeal held, that because O'Hara lacked the feature of "flexibly biasing the plenum against the drum", there was no infringement. More importantly, the Court said that it could not rewrite the patent claim to omit the feature that was later discovered to be unnecessary.

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"A court must interpret the claims; it cannot redraft them. When an inventor has clearly stated in the claims that he considered a requirement as essential to his invention, a court cannot decide otherwise for the sole reason that he was mistaken." (53)

Equitable Infringement

Equitable infringement is invoked when the claim is narrower than the invention that could have been claimed, validly, by the inventor. The court exercises its equitable jurisdiction to "stretch" the exact language of the claim to either ignore the unnecessary claim element or to substitute equivalents for the elements.

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For example, imagine a claim reciting four elements:

It is clear that the fourth element is unnecessary for the proper functioning of the invention. The patent drafter should never have included the element in the claim. Who is to pay for that mistake?:

• the inventor, by having the monopoly limited to sailboards having green pennants?

• the infringer, by having the courts ignore that limitation and find there to be infringement even if no green pennant is present? or

• the patent agent who perhaps negligently included an unnecessary element?

In effect, under the equitable infringement cases, the Court rewrites the claim, to a more abstract description of the invention to a higher level of abstraction than was chosen by the inventor or the patent agent when the patent was sought. The element is either eliminated altogether or a functional equivalent is substituted.

In Canada, the Courts do not admit that they are rewriting the claims. Like the Emperor with new clothes, they appear to be the last to recognize (or admit) what is happening.

Pith and substance

The leading case in Canada for infringement of the "pith and substance" of a patent is McPhar v. Sharpe(54).

In the McPhar case, the claims called for "... means to suspend said transmitting coil to hang freely in a vertical plane but orientable in azimuth..." and "... a transmitting coil suspended to hang vertically and orientable in azimuth".

The defendant mounted its coil on top of a tripod, allowing free rotation about the azimuth (vertical axis).

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The Court held that there was infringement under the "pith and substance" doctrine.

Under the "pith and substance" doctrine, the claim is analyzed and divided into two sets of elements: those that are deemed "essential" and those that are deemed "non-essential". Variations or omissions of non-essential elements do not change the way the invention works. One is considered to have taken the substance of the invention if one uses all the essential elements; non-essential elements can be omitted or varied.

Since form follows function, any change to the elements of the patent will, in some way, change how the invention works - unless the element is as frivolous as the green pennant example given above. A more proper question to ask is whether the change to the way the invention works is, for all practical purposes, negligible.

The doctrine of "pith and substance" flies in the face of the case law that says that the Court can only interpret, and must not rewrite the claims.(55) Likewise, it prevents there being a clear "fence" surrounding the invention (one of the purposes of claims) so that others can avoid infringement. The doctrine of "pith and substance" has created the most uncertainty as to the scope of a patent (and thus spawned considerable litigation).

The leading cases dealing with "pith and substance" include:

"The infringer might not take the whole of the instrument here described, but he might take a certain number of parts of the instrument described; he might take an instrument which in many respects would resemble the patent instrument, but would not resemble it in all its parts. And there the question would be, ..., whether that which was done by the alleged infringer amounted to a colourable departure from the instrument patented, and whether in what he had done he had not really taken and adopted the substance of the instrument patented. And it might well be, that if the instrument patented consisted of twelve different steps,..., an infringer who took eight or nine or ten of those steps might be held by the tribunal judging of the patent to have taken in substance the pith and marrow of the invention, although there were one, two, three, four or five steps which he might not actually have taken and represented upon his machine."

"The principle is, indeed, no more than a particular application of the more general principle that a person who takes what in the familiar, though oddly mixed metaphor is called the pith and marrow of the invention is an infringer. If he takes the pith and marrow of the invention he commits an infringement even though he omits an unessential part. So, too, he commits an infringement if, instead of omitting an unessential part, he substitutes for that part a mechanical equivalent."

It should be noted that while the inclusion of claims became compulsory in the U.K. in 1883, the specification in Adie ended with a single general claim. The specification in RCA ended with a full list of claims. As mentioned above, the statutory requirement that patents end with claims was introduced to the Canadian Patent Act by 1923 (s.14, The Patent Act, S.C. 1923, c.23).

The doctrine of equivalents therefore allows one to claim one member of a species (which species contains equivalents of what has been claimed) but obtain protection for the next higher order - the genus.

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For example, one could claim, as a claim element, a bolt. Mechanical equivalents would include a nail and a rivet. These fasteners would be part of the genus "fastener". Thus the Court rewrites the claim to one level of abstraction higher than that contemplated by the patent drafter.

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Catnic's "purposive construction"

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In the Catnic(56) case, the Catnic patent called for a lintel (the bar that goes across the top of a window to support the weight of the bricks laid above it) to have a rear wall member which should "extending vertically". A cross-sectional view of the Catnic lintel from the Catnic patent drawings is shown in Figure 1 to the left. The rear wall is highlighted in yellow.

Hill copied the Catnic design, then after receiving a writ from Catnic, changed the design so that the rear member was inclined 6 or 8 degrees from the vertical. This resulted in the Hill lintels being 0.6 or 1.2 per cent weaker in their load bearing capacities. Functionally, this was a negligible difference, rendering the lintel only slightly weaker than the one shown in the patent. The Hill lintel is shown in Figure 2, with the inclined rear wall contained in the yellow highlighting.

The Trial Judge, Whitford J., held that there was no literal infringement but there was infringement under the "pith and marrow" doctrine. The Court of Appeal held that the limitation that the rear member should "extend vertically" was an essential feature and there could be no infringement of the "pith and marrow".

The House of Lords attempted to end the "pith and substance" test and replace it with new simpler test: "purposive construction".

1. Does the element at issue affect the way the invention works?

2. If it obviously does not, is it clear from a reading of the patent that the inventor did not intend to limit the invention to exclude a variant of the element?

If the second question is answered in the affirmative, then the variant is permitted and the infringement is caught.  The second part of the test is a difficult one to apply since its formulation combines a negative with an intention to exclude. The patent drafter would be trying to draft what was intended to be included rather than what to exclude. All non-included matters might not have been thought of at all.(56a)

The Improver(57) case tried to undo the double negative and express the second element of the test as a positive:

"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."

The new test became an inelegant rephrasing of the "pith and substance" test. The double negative language makes the test extremely difficult to apply.

Lord Diplock's judgment contains some bizarre twists of purported logic, which may explain the tortured test he created.

Lord Diplock first recited the language reminiscent of EMI v. Lissen at p. 242-3:

"My Lords, 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."

This language sounds like what patent drafters are trying to achieve: claiming only what is essential to the invention.

Lord Diplock continued at p. 243:

"It is those novel features only that he claims to be essential that constitute the so-called "pith and marrow" of the claim."

What does this mean? Does it mean that the claim and the "pith and marrow" of the patent are coterminous? Or does it mean that the essential parts of the claim (some subset of the whole, excluding the non-essential parts of the claim) is the "pith and marrow" of the claim or invention? Given Lord Diplock's later "logic", discussed below, where he divides the claim elements into two categories: those that were not intended to be varied and those that were), for his judgment to be logically consistent, Lord Diplock must have meant the latter.

Lord Diplock appears to have said that there is no use in treating literal infringement and infringement of the "pith and marrow" as separate causes of action - there is only infringement:

"... 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 invasion. There is, in my view, no such dichotomy; there is but a single cause of action and to treat it otherwise, particularly in cases like that which is the subject of the instant appeal, is liable to lead to confusion."

The point appears to be merely semantical: Lord Diplock envisages a test for when there is a variant from what is claimed (so there must be another test when there is no variant from what is claimed: literal infringement). Whether there is a separate cause of action or not, there are two different tests for literal and non-literal infringement, the latter being articulated in Catnic.

Lord Diplock should have then asked, "What would a skilled reader of the patent have understood to be included in the term 'extending vertically'?" Given the comments made above with respect to the precision of engineering, the answer should have been: "vertical plus or minus a few degrees".

Lord Diplock may have been trying to express that concept in the Catnic case when he said tortuously at pp. 242-243:

"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 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."

Lord Diplock then analyzed the previous cases of the House of Lords dealing with claim construction and identified the issues upon which the cases turned:

At page 244, Lord Diplock's comment seems to confirm that he considered the "essential features" of the invention to be a subset of all the features in the claim:

"The essential features of the invention that is the subject of claim 1 of the patent in suit in the instant appeal are much easier to understand than those of any of the three patents to which I have just referred; and this makes the question of its construction simpler."

"Strict compliance" with a phrase such as "extending vertically" would probably have meant, in Lord Diplock's mind, "vertical plus or minus zero degrees" - engineering-wise a technical impossibility, as indicated by his comments at page 244:

"Put in a nutshell the question to be answered is: Would the specification make it obvious to a builder familiar with ordinary building operations that the description of a lintel in the form of a weight-bearing box girder of which the back plate was referred to as "extending vertically" from one of the two horizontal plates to join the other, could not have been intended to exclude lintels in which the back plate although not positioned at precisely 90 degrees to both horizontal plates was close enough to 90 degrees to make no material difference to the way the lintel worked when used in building operations? 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, since any imitator could avoid it and take all the benefit of the invention by the simple expedient of positioning the back plate a degree or two from the exact vertical.

It may be that when used by a geometer addressing himself to fellow geometers, such expressions descriptive of relative position as "horizontal", "parallel", "vertical" and "vertically" are to be understood as words of precision only; but when used in a description of a manufactured product intended to perform the practical function of a weight-bearing box girder in supporting courses of brickwork over window and door spaces in buildings, it seems to me that the expression "extending vertically" as descriptive of the position of what in use will be the upright member of a trapezoid-shaped box girder, is perfectly capable of meaning positioned near enough to the exact geometrical vertical to enable it in actual use to perform satisfactorily all the functions that it could perform if it were precisely vertical; and having regard to those considerations to which I have just referred that is the sense in which in my opinion "extending vertically" would be understood by a builder familiar with ordinary building operation." [emphasis added]

What Lord Diplock was really saying was that for all practical purposes of the lintel, the Hill rear wall was "extending vertically". No one patenting or building lintels (the persons to whom the patent is addressed) would ever consider that the rear wall had to be exactly vertical: it could be built within such limits (ie. degrees off vertical) that did not significantly alter its functionality. Given such a method of claim construction, the Hill rear wall fit within the meaning the term would have in the context of the art of the Catnic patent to a person skilled in the art. To paraphrase the last sentence of the paragraph quoted above: It is obvious to the skilled reader that the patentee meant "vertical within a small range of degrees". At this point, Lord Diplock had gotten it right, but then veered off the mark.

He continued:

"Or, putting the same thing in another way, it would be obvious to him that the patentee did not intend to make exact verticality in the positioning of the back plate an essential feature of the invention claimed."

Lord Diplock should have asked: "To a skilled reader of the patent, did "extending vertically" include within its meaning in the context of the patent, vertical to within 6 degrees?"

In his mind, the six degree off vertical of the Hill lintel's rear wall was a variant from what was claimed ("extending vertically"). This required him to engage in some tortured logic to find a test for construction and infringement; the double negative test of the patent having to show no intention to exclude such a variant.

  McPhar   Catnic
  "pith and substance" "purposive construction"
elements that when varied, do change the way the invention works essential  

"strict compliance was intended to be essential"

elements that when varied, don't change the way the invention works non-essential

variants of elements not intended to be excluded

So what is the difference between the "pith and substance" test of the line of cases leading to and from McPhar v. Sharpe and the Catnic test? For all practical purposes, they are the same.(59)

In both tests the claims are divided into two classes of elements: those that the Court will allow to be varied and those they will not. The elements that can be varied ("non-essential" elements in the "pith and substance" test and "elements not intended to be excluded" in the Catnic test) do not change the way the invention works; the ones that cannot be varied ("essential") or do change the way the invention works.

So although Lord Diplock may have been right when he said there are not two separate causes of action for 'literal infringement' and infringement of the 'pith and marrow', he certainly appears to have created a test for situations in which there is a variant from what is claimed. Is it not the case then, that when there is no variant from what is claimed we are in a situation of literal infringement?

And after stating that there is no separate cause of action for infringement of the 'pith and substance', Lord Diplock recreates the same test in different language: a test of construction based not on what the claim would say to a skilled worker, but one based upon the functional contribution of certain elements and essentially writing a new claim with only the "essential" elements present.

Lord Diplock certainly did get one part of his judgment right:

"...there is but a single cause of action and to treat it otherwise, particularly in cases like that which is the subject of the instant appeal, is liable to lead to confusion."

Catnic has been interpreted as being a case dealing with variants, when, in fact, it was dealing with the precision of the words in their context. Even if the Catnic case was one dealing with a situation where there was a variant from what was claimed, what possible general application could the Catnic test have in situations where there is no variant (ie. cases of literal infringement)? I say: none. A more general rule of claim construction is therefore required.

The U.S. Doctrine of Equivalence

The U.S Courts have developed a claim interpretation method similar to that of "pith and substance" called the "doctrine of equivalents".

In Winans v. Denmead(60) the doctrine of equivalents was described as growing out of a legally-implied term in each patent claim that "... the claim extends to the thing patented, however its form or proportions may be varied." In Winans, the majority held that "... to copy the principle or mode of operation described, is an infringement, although such copy should be totally unlike the original in form or proportions."(61)

In Graver Tank Mfg. Co. v. Linde Air Products Co.(62), the U.S. Supreme Court articulated the "doctrine of equivalents". Under the doctrine, a product or process that does not literally infringe the express terms of a patent claim can nevertheless be found to infringe if there is an equivalence between the elements of the accused product or process and the claimed elements of the patented invention. In Graver Tank, the defendant's chemical composition for use in welding differed from the patented welding material by the substitution of one chemical element.(63) The substituted element did not fall within the literal terms of the patent claim.

"What constitutes equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case. Equivalence, in the patent law, is not the prisoner of a formula and is not an absolute to be considered in a vacuum. It does not require complete identity for every purpose and in every respect. In determining equivalents, things equal to the same thing may not be equal to each other and, by the same token, things for most purposes different may sometimes be equivalents. Consideration must be given for the purpose for which an ingredient is used in a patent, the qualities it has when combined with the other ingredients, and the function which it is intended to perform. An important factor is whether persons reasonably skilled in the art would have known of the interchangeability of an ingredient not contained in the patent with one that was."(64)

Thus, the claim element's purpose, qualities and function must be determined and the equivalent must be predictably interchangeable with the claimed element.

The test has been summarized as: Does the accused device " ... perform substantially the same overall function or work, in substantially the same way, to overcome substantially the same overall result as the claimed invention?"(65)

In 1997, in the Hilton Davis case, the U.S. Supreme Court clarified the scope of the doctrine of equivalents.

The Hilton Davis patent related to a purification process. Impure dyes were passed through a porous membrane at certain pressures and pH levels, resulting in a high purity product. The claim required the pH to be "... at a pH from approximately 6.0 to 9.0". The prior art disclosed an ultrafiltration process operating at a pH above 9.0. There was disagreement as to why the low-end pH limit of 6.0 was included in the claim. Warner-Jenkinson used an ultrafiltration process that operated at a pH of 5.0.

Justice Thomas stated (at p. 6 of 19):

"We do, however, share the concern of the dissenters below that the doctrine of equivalents, as it has come to be applied since Graver Tank, has taken on a life of its own, unbounded by the patent claims. There can be no denying that the doctrine of equivalents, when applied broadly, conflicts with the definitional and public-notice functions of the statutory claiming requirements."

Recognizing that the courts have no right to enlarge a patent beyond the scope of its claims as allowed by the Patent Office, the court adopted an "all-elements" test:

"Each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole. It is important to ensure that the application of the doctrine, even as to an individual element, is not allowed such broad play as to effectively eliminate that element in its entirety."

In the Warner-Jenkinson Co. Inc. v. Hilton Davis Chemical Co.(66) case, although the lower limit of approximately 6.0 became a material element of the claim, it did not necessarily preclude the application of the doctrine of equivalents as to that element.

In Hilton Davis, the court held that:

"The known interchangeability of substitutes for an element of the patent is one of the express objective factors noted by Graver Tank as bearing upon whether the accused device is substantially the same as the patented invention." (at p. 12 of 19)

The court recognized that the "function, way, result" test was suitable for analysing mechanical equivalents but often provided a poor framework for analysing other products or processes. The court held (at p. 15 of 19):

"In our view, the particular linguistic framework used is less important than whether the test is probative of the essential enquiry: does the accused product or process contain elements identical or equivalent to each claimed element of the patented invention? ... A focus on individual elements and a special vigilance against allowing the concept of equivalents to eliminate completely any such elements should reduce considerably the imprecision of whatever language is used. An analysis of the role played by each element in the context of the specific patent claim will thus inform the enquiry as to whether a substitute element matches the function, way and result of the claimed element, or whether the substitute element plays a role substantially different from the claimed element."


US section 112(6): means-plus-function claims

Section 112(6) has been described as a 'reverse doctrine of equivalents'.(67) If an element in a claim is described as a means for performing a certain function (called a "means plus function" claim element), theoretically, that claim element could encompass any means of performing the function.

In 1952, the United States enacted s. 112(6) that provided:

"An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material or acts in support thereof, and such claims shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof."

The patentee must describe in the disclosure, some structure that performs the claimed function. The claim will then be limited to the structure, material or acts in the disclosure, and their equivalents. The section has no effect on the function specified - it does not extent the element to equivalent functions.(68)

In contrast, a structural claim limitation (claiming a "thing") includes the specific structure disclosed in the patent specification as well as other structures not disclosed in the patent which are aptly, literally described by the structural language of the claim.

Generally, new elements that use the term " means" or "means for" are presumably functional. Using the term "means" generally invokes Section 112(6).(69)

The presumption that "means" denotes a functional claim element is rebutted when the claim element as a whole is primarily structural. The Court will ask, does the claim language following "means" state the function or instead does it recite structure. Without an identified function, the term "means" in the claim cannot invoke Section 112(6). Without a means sufficiently connected to a recited function, the presumption does not operate.(70) For example the use of the phrase "perforation means" should not invoke section 112(6).

Unless one wants Section 112(6) to be invoked, functions performed by structural elements should be avoided.

Section 112(6) can also be applied to method claims because the section states that an element may be expressed as a step for performing a particular function. Section 112(6) applies to "steps" (the generic description of elements of a process) but not "acts" (the implementation of such steps).(71) It has been recommended that using unnecessary introductory language such as "the method comprising the steps of" should be avoided. Otherwise it may unnecessarily invite a Court to interpret the method claim under 112(6).(72)

U.S. Patent Attorney Randy Beckers recommends that means-plus-function claims be used in an aggressively drafted set of claims: i.e.(73)

The means-plus-function claims would be helpful in a lawsuit to maintain the validity of the claims over newly discovered prior art. The limitations found in the disclosure could be used to distinguish over new prior art.

A "Precise" test for claim construction

It is the premise of this paper that the "purposive construction" test of Catnic and the "pith and substance" test of McPhar are awkward, unpredictable and contradictory to overriding fundamental principles of patent law. They have resulted in Courts determining whether there has been infringement of the "equity" of the patent. This has resulted in an unpredictability in the Courts which fosters litigation, only to the benefit of litigators and to the detriment of defendants.

I recommend that these tests be abandoned and be replaced a new, more simple test that achieves the same outcome of many of the past decisions. In cases where the new test does not achieve the same outcome as the "pith and substance" or Catnic's "purposive construction", I submit that it underlines the inherent problems with the previous tests.

The test is dubbed "the Precision Test" and to determine infringement, is executed in two steps: (1) claim construction and (2) infringement.

1. The "Precise Claim Construction" test is:

In the context of the patent, with what degree of precision is the word or phrase used?

2. The "Precise Infringement Test" is:

Does the claim, with those words or phrases, so construed, aptly described the alleged infringement?

This test is consistent with most other principles of construction and infringement, more so than the McPhar or Catnic tests, namely:

The proposed Precise test is more one of literal construction, recognizing that the patent drafter has the ability to choose the language of the patent, to the highest level of abstraction desired, and that it is up to the Court to interpret the language used, not to rewrite the claim


Applying the "Precise" test to the facts of Catnic, what the Courts should have been asking was:

1. "What did the inventor mean when he used the term 'extending vertically' to describe the orientation of the rear wall of the lintel. With what degree of precision was the inventor using that word?

In the context of mechanical devices, they are all made to certain design tolerances so the term "vertical" must have been meant to include absolutely vertical (ie. 90 degrees from absolutely horizontal) plus or minus a few degrees. The six degree offset of the Hill lintel rear wall did not significantly alter the way the lintel worked. For all practical purposes, "extending vertically" would include a few degrees off vertical and, as understood by Lord Diplock would have been so understood by a skilled reader of the patent (an engineer).

2. Does the claim, with those words or phrases, so construed, aptly described the alleged infringement?

The definition of "extending vertically" being broad enouigh to include something a few degrees off vertical, would include the Hill rear wall, which would thereby be an infringement.

Cutter (Canada) Ltd. v. Baxter Travenol Laboratories of Canada Ltd. et al(74)

The Baxter patent claims called for a cannula (tube) to puncture a membrane and allow fluid passage between the two sections of the blood bag. The Cutter device had a spike which puncture the membrane.

cutter.gif (29573 bytes)

The Court of Appeal held that there was infringement by the taking of the pith and substance of the patent.

"It seems to me to be plain that the Cutter spike is, as found by the learned trial judge, the functional equivalent of the cannula referred to in claims 1, 2 and 4. Both are operated by the technician in the same way. Both rupture the membrane and establish a channel or channels through which blood or its components or anticoagulants can flow. Both do it in the same way. The evidence shows that the cannula ruptures the membrane by causing a transverse slit which permits the blood to flow around the outside wall of the cannula as well as through its lumen.

Moreover, both devices are in the tube and are unattached.

Further, in my view, the precise structure or configuration of the device to be used to rupture the membrane and establish a flow channel is not an essential element of the invention. As I see it, it would not matter whether a cannula or a vaned spike or a device of some other sort, such as, for example, a device of the like proportions with a semicircular cross section, were used or whether it would cut out in whole or in part or merely rupture the membrane. The substance of the invention, its "pith and marrow", would be taken so long as the rupturing device had the essential elements of being in the tube and being unattached. I think therefore that the substance of the invention has been taken and that all the claims of the patent were infringed by the Cutter device."(75)

Obviously, a spike is not a tube. The Court of Appeal rewrote the claim, changing its language and scope.

Under the Precise test, the case would have failed because a spike is not a tube. Had Baxter wanted to protect a spike, it should have claimed a "membrane piercing means".


1. quoted by Tom Lewis in "Empire of the Air, The Men Who Made Radio"; Edward Burlingame Books, 1991 referring to his losses in the hands of the U.S. judicial system. Mr. Armstrong committed suicide by jumping out of his 13th floor apatment building in New York City on February 1, 1954. By 1967, Marion Armstrong, Edwin Armstrong's widow had won the last of all of Armstrong's FM patent lawsuits.

2. R.S.C. 1985, c. P-4, as amended.

3. B.V.D. Company Ltd. v. Canadian Celanese Ltd., [1937] S.C.R. 221 (per Davis, J.) at p. 233.

3a. In Australia, several judges have held that the term "comprising" doesn't mean "includes" but rather means "consists of ... and not others" or "is limited to".  See Asahi Kasei Kogyo Kabushiki Kaisha v. W.R. Grace & Co. (1991) 22I.P.R. 491 (F.C. per Heerey J.); N.V. Phillips Gloeilampenfabrieken v. Mirabella International Pty. Ltd. (1993) 26 I.P.R. 513 (F.C.); General Clutch Corporation v. Sbriggs Pty. Ltd. (1997) 30 I.P.R. 359 (F.C. per Lindgren J.)

4. Minerals Separation North America Corporation v. Noranda Mines Ltd. [1947] Ex. C.R. 306 (per President Thorson) at pp. 352-3 affirmed (1949), 12 C.P.R. 99 per Kelloch J. at p. 202 (S.C.C.).

5. Electric and Musical Industries, Ltd. et al v. Lissen, Ltd. et al (1939), 56 R.P.C. 23 (per Lord Russell of Killowen) at p. 39; Lovell Manufacturing Co. v. Beatty Bros. Ltd. (1962), 41 C.P.R. 18 (Ex.Ct) Per Thomson P. at p. 70-71

6. Dableh v. Ontario Hydro (1996) 68 C.P.R. (3d) 129 (F.C.A. per Strayer J.) (Linden and Robertson J.J.A. concurring) at p. 143.

7. Dableh v. Ontario Hydro (1996) 68 C.P.R. (3d) 129 (F.C.A. per Strayer J.) (Linden and Robertson J.J.A. concurring) at p. 142-143

8. American Cyanamid Co. v. Berk Pharmaceuticals Ltd., [1976] R.P.C. 231 (Ch.D.) at p. 234; Xerox of Canada Ltd. et al v. IBM Canada Ltd. (1977) 33 C.P.R. (2d) 24 (F.C.T.D. per Collier, J.) at p. 43

9. Western Electric Co. Inc. et al v. Baldwin International Radio [1934] S.C.R. 570 at p. 572; Lovell Manufacturing Co. v. Beatty Bros. Ltd. (1962), 41 C.P.R. 18 (Ex.Ct) Per Thomson P. at p. 70-71; (1962) Fox Pat. C. 112 at 126.

10. Markman v. Westview Instruments, Inc., 116 S. Ct. 1384 (1996)

11. Rodi & Wienenberger (1969) R.P.C. 367 (H.L. per Lord Upjohn) at p. 391(1); Burton Parsons v. Hewlett Packard (1975), 17 C.P.R. (2d) 97 (S.C.C per Pigeon J.) at p. 104

12. The General Tire & Rubber Company v. The Firestone Type and Rubber Company Limited and Others [1971] R.P.C. 173 (per Graham, J.) [1972] R.P.C. 457 at 439(2); American Cyanamid Company v. Ethicon Limited [1979] R.P.C. 215 (per Graham, J.) at p. 245-246

13. American Cyanamid Co. v. Berk Pharmaceuticals Ltd., [1976] R.P.C. 231 (Ch.D.) at p. 234(3)

14. Burton Parsons v. Hewlett Packard (1975), 17 C.P.R. (2d) 97 (S.C.C per Pigeon J.) at p. 104

15. The Edison Bell Phonograph Corporation, Limited v. Smith and Young [1894] 11 R.P.C. 389 at p. 396(1)

16. Lubrizol Corp. v. Imperial Oil Ltd. (1990) 33 C.P.R. (3d) 1 (F.C.T.D.) at p. 12-13.; aff'd (1992), 45 C.P.R. 9(3d) 449 (F.C.A.) at p. 467

17. Reliance Electric Industrial Company et al v. Northern Telecom Limited (1993) 47 C.P.R. (3d) 55 (F.C.T.D. Per Reed J.) at p. 61

18. British Celanese, Ltd. v. Courtaulds, Ltd. (1935), 52 R.P.C. 171 (per Lord Tomlin) at p. 196

19. Xerox of Canada Ltd. et al v. IBM Canada Ltd. (1977) 33 C.P.R. (2d) 24 (F.C.T.D. per Collier, J.) at p. 36-37.

20. AlliedSignal Inc. v. Du Pont Canada Inc. et al (1995), 61 C.P.R. (3d) 417 (F.C.A. per Desjardins J.A.) At p. 426

21. Lister v. Norton Brothers and Co. [1886] 3 R.P.C. 199 at p. 203

22. Henriksen v. Tallon Limited [1965] R.P.C. 434 at 446; Consolboard Inc. v. MacMillan Bloedel (Sask) Ltd. (1981) 56 C.P.R. (2d) 145 (S.C.C. per Dickson J.) at p. 157

23. Western Electric Co. Inc. et al v. Baldwin International Radio [1934] S.C.R. 94 at p. 133

24. Henriksen v. Tallon Limited [1965] R.P.C. 434; Consolboard Inc. v. MacMillan Bloedel (Sask) Ltd. (1981) 56 C.P.R. (2d) 145 (S.C.C. per Dickson J.) at p. 157

25. Rodi & Wienenberger (1969) R.P.C. 367 (H.L. per Lord Upjohn)at p. 391; Dableh v. Ontario Hydro (1996) 68 C.P.R. (3d) 129 (F.C.A. per Strayer J.) (Linden and Robertson J.J.A. concurring)at p.143.

26. Lovell Manufacturing Co. v. Beatty Bros. Ltd. (1962), 41 C.P.R. 18 (Ex.Ct) Per Thomson P. at p. 33; Ransbury Co. v. Aerostyle Ltd. [1968] R.P.C. 287 at 297 per Lord Upjohn.

27. O'Hara Manufacturing Ltd. et al v. Eli Lilly & Co. et al (1989), 26 C.P.R. (3d) 1 (F.C.A. per Pratte J.A.) T p. 7.

28. Lister v. Norton Brothers and Co. [1886] 3 R.P.C. 199 at p. 203

29. Western Electric Co. Inc. et al v. Baldwin International Radio [1934] S.C.R. 570 at p. 582; Minerals Separation North American Corp. v. Noranda Mines, Ltd. (1947), 12 C.P.R. at p. 102 per Thorson p. 185-188; Electric and Musical Industries, Ltd. et al v. Lissen, Ltd. et al (1939), 56 R.P.C. 23 (per Lord Russell of Killowen) at p. 41

30. AlliedSignal Inc. v. Du Pont Canada Inc. et al (1995), 61 C.P.R. (3d) 417 (F.C.A. per Desjardins J.A.)

31. United Merchants and Manufacturers Inc. v. A.J. Freiman Limited et al (1965) 47 C.P.R. 97 per Noel, J. (Ex. Ct.) at p. 108

32. Henriksen v. Tallon Limited [1965] R.P.C. 434 at p. 446.

33. Noranda Mines Ltd. v. Minerals Separation North American Corp. (1949) 12 C.P.R. 99 per Rand, J. (S.C.C.) at p. 36; Beecham Canada Ltd. v. Procter & Gamble Co. (1982) 61 C.P.R. (2d) 1 (F.C.A. per Urie J.A.) At p. 8-11; British Hartford-Fairmont Syndicate, Ltd. v. Jackson Bros. (Knottingley), Ltd. 49 R.P.C. 495, per Romer J. at p. 556

34. Minerals Separation North American Corp. v. Noranda Mines, Ltd. (1947), 12 C.P.R. at p. 102 [1947] Ex. C.R. 306 , 6 Fox Pat. Co. 130 per Thorson P. at p. 185

35. Ingersoll Sargeant Drill Co. v. Consolidated Pneumatic Tool Co. Ltd. (1907) 25 R.P.C. 61 per Sir Mark Romer at p. 83; Electric and Musical Industries, Ltd. et al v. Lissen, Ltd. et al (1939), 56 R.P.C. 23 (per Lord Russell of Killowen) at p. 41

36. British Hartford-Fairmont Syndicate, Ltd. v. Jackson Bros. (Knottingley), Ltd. 49 R.P.C. 495, per Romer J. at p. 556.

37. Electric and Musical Industries, Ltd. et al v. Lissen, Ltd. et al (1939), 56 R.P.C. 23 (per Lord Russell of Killowen) at p. 43

38. (Natural Colour at p. 266; Noranda Mines Ltd. v. Minerals Separation North American Corp. (1949) 12 C.P.R. 99 per Rand, J. (S.C.C.); Mullard Radio Valve Co. Ld. v. Philco Radio and Television Corporation of Great Britain, Ld. and Others (1936) 53 R.P.C. 323 (H.L. per Lord MacMillan) at p. 352

39. Fox, Harold; "The Canadian Law and Practice Relating to Letters Patent for Inventions" at p. 217 referring to Clippens v. Henderson (1882), 10 R. (Ct. of Sess) 38, (1883), 8 App. Cas. 873; Lister v. Dix (1899), 16 R.P.C. 89.

40. Lovell Manufacturing Co. v. Beatty Bros. Ltd. (1962), 41 C.P.R. 18 (Ex.Ct) Per Thomson p. 134; Dableh v. Ontario Hydro (1996) 68 C.P.R. (3d) 129 (F.C.A. per Strayer J.) (Linden and Robertson J.J.A. concurring)

41. B.V.D. Company Ltd. v. Canadian Celanese Ltd. [1937] S.C.R. 221 (per Davis, J.) at p. 236-237

42. Molins and Molins Machine Co., Ltd. v. Industrial Machinery Co., Ltd. (1938) 55 R.P.C. 31 per Greene, M.R. (C.A.) at p. 39; Amfac Foods Inc. et al v. Irving Pulp & Paper, Ltd. (1987) 12 C.P.R. (3d) 193 (F.C.A. per Urie J.) at p.205.

43. Canadian General Electric Co., Ld. v. Fada Radio Ltd. [1929] 47 R.P.C. 69 (H.L.) at p. 90

44. Johnson Controls, Inc. v. Varta Batteries Ltd. (1984) 80 C.P.R. (2d) 15 at p. 27-28.

45. Lovell Manufacturing Co. v. Beatty Bros. Ltd. (1962), 41 C.P.R. 18 (Ex.Ct) Per Thomson P. at p. 37-38; O'Hara Manufacturing Ltd. et al v. Eli Lilly & Co. et al (1989), 26 C.P.R. (3d) 1 (F.C.A. per Pratte J.A.) at p.7.

46. Reliance Electric Industrial Company et al v. Northern Telecom Limited (1993) 47 C.P.R. (3d) 55 (F.C.T.D. Per Reed J.) at p.64.

47. Molins and Molins Machine Co. Ltd. v. Industrial Machinery Co. Ltd. (1938), 55 R.P.C. 29 at 31; Dableh v. Ontario Hydro.

48. Lovell Manufacturing Co. v. Beatty Bros. Ltd. (1962), 41 C.P.R. 18 (Ex.Ct) Per Thomson P. at p. 122-134 especially p. 131-132 and 134

49. Ductmate Industries Inc. v. Exanno Products Ltd. (1984) 2 C.P.R. (3d) 289 per Reed J. (F.C.T.D) at p. 308-309

50. Amfac Foods Inc. et al v. Irving Pulp & Paper, Ltd. (1987) 12 C.P.R. (3d) 193 (F.C.A. per Urie J.) at p. 86-87

51. (1939), 56 R.P.C. 23

52. O'Hara Manufacturing Ltd. et al v. Eli Lilly & Co. et al (1989), 26 C.P.R. (3d) 1 (F.C.A. per Pratte J.A.)

53. O'Hara Manufacturing Ltd. et al v. Eli Lilly & Co. et al (1989), 26 C.P.R. (3d) 1 (F.C.A. per Pratte J.A.) T p. 7.

54. McPhar Co. v. Sharpe Instruments (1960), 21 Fox Pat. C. 1

55. O'Hara Manufacturing Ltd. et al v. Eli Lilly & Co. et al (1989), 26 C.P.R. (3d) 1 (F.C.A. per Pratte J.A.) at p. 7.

56. Catnic Components Ltd. v. Hill & Smith Ltd. (1982) R.P.C. 183 (H.L. per Lord Diplock)

56a.Daily v. Etablissements Fernard Berchet [1993] R.P.C. 357 at p. 363 (U.K. C.A.)

57. Improver v. Remington Consumer Products Ltd. [1989] R.P.C. 679 (C.A.)

58. [1977] F.S.R. 215; [1978] R.P.C. 153

59. Procter & Gamble Co. v. Kimberley-Clark of Canada Ltd. (1991) 40 C.P.R. (3d) 1 (F.C.T.D. per Teitelbaum) at p. 18-21.

60. 15 How. 330, 343 (1854)

61. Winans, supra, at 341-42

62. 339 U.S. 605 (1950)

63. ibid at p. 610

64. ibid at p. 609

65. Pennwalt Corp. v. Durand-Wayland, Inc., 833 f.2d 931, 934 (Fed. Cir. 1987)

66. Warner-Jenkinson Co. Inc. v. Hilton Davis Chemical Co., [1997] SCT-QL 50.

67. Johnston v. IVAC Corp., 12 U.S.P.Q. 2d 1382, 1386 (Fed. Cir. 1989)

68. Johnston v. IVAC Corp., 12 USPQ2d 1382, 1382, 1386 (Fed. Cir. 1989)

69. Greenberg v. Ethicon Endo-Surgery, Inc., 91 F.3d 1580, 39 USPQ2d 1783 (Fed. Cir. 1996)

70. York Products, Inc. v. Central Tractor Farm & Family Center, 99 F.3d 1568, 40 USPQ2d 1619 (Fed. Cir. 1996) at p. 1624 see also Cole v. Kimberly Clark Corp., 102 F.3d 524, 41 USPQ2d 1001 (Fed. Cir. 1996)

71. O.I. Corporation v. Tekmar Company, Inc., 42 USPQ2d 1777 (Fed. Cir. 1997) p. 1781-82. Caterpillar Inc. v. Detroit Diesel Corp., 41 USPQ2d (N.D. Ind. 1996)

72. Don Muirhead and John Gorecki, "Recent Decisions Clarifying Interpretation of Functional Claim Elements in U.S. Patents"; Foley, Hoag & Eliot LLP Patent Update July 1997 p. 4

73. J. Randall Beckers; "Patent Prosecution Basics: Means - Plus - Function - What is it good for?"; Staas & Halsey News Letter, 1998.

74. (1983) 68 C.P.R. (2d) 179.

75. (1983) 68 C.P.R. (2d) 179 at pp.198-199 .