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A Comparative Analysis regarding Patent Claim Construction : The English Purposive Construction and the US Doctrine of Equivalents. Dr Jakkrit Kuanpoth Tilleke & Gibbins International. Patent infringement. Lessons from validity It’s the claim that counts!

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A Comparative Analysis regarding Patent Claim Construction : The English Purposive Construction and the US Doctrine of Equivalents

Dr Jakkrit Kuanpoth

Tilleke & Gibbins International

patent infringement
Patent infringement
  • Lessons from validity
    • It’s the claim that counts!
  • Comparing claim to [reference] = comparing claim to [accused product]
the telephone cases 1888

Claim at issue: “The method of, and apparatus for, transmitting vocal or other sounds telegraphically, as herein described, by causing electrical undulations, similar in form to the vibrations of the air accompanying the said vocal or other sounds, substantially as set forth.”

The Telephone Cases (1888)

พระราชบัญญัติสิทธิบัตร พ.ศ. ๒๕๒๒มาตรา ๓๖ ทวิ
  • “สิทธิของผู้ทรงสิทธิบัตรตามมาตรา ๓๖ ในการประดิษฐ์ที่ได้รับสิทธิบัตรมีขอบเขตดังระบุในข้อถือสิทธิ ในการวินิจฉัยขอบเขตของการประดิษฐ์ตามข้อถือสิทธิ ให้พิจารณาลักษณะของการประดิษฐ์ที่ระบุในรายละเอียดการประดิษฐ์และรูปเขียนประกอบด้วยขอบเขตของการประดิษฐ์ที่ได้รับความคุ้มครองย่อมคลุมถึงลักษณะของการประดิษฐ์ที่แม้จะมิได้ระบุในข้อถือสิทธิโดยเฉพาะเจาะจง แต่เป็นสิ่งที่มีคุณสมบัติประโยชน์ใช้สอย และทำให้เกิดผลทำนองเดียวกับลักษณะของการประดิษฐ์ที่ระบุไว้ในข้อถือสิทธิตามความเห็นของบุคคลที่มีความชำนาญในระดับสามัญในศิลปะหรือวิทยาการที่เกี่ยวข้องกับการประดิษฐ์นั้น”

Comparison of:

Claimed Invention and Accused Device

• Literal (Purposive Construction)

• Non-Literal (Doctrine of Equivalents)

electric and musical industries ltd et al v lissen ltd et al 1939
Electric and Musical Industries, Ltd. et al v. Lissen, Ltd. et al (1939)
  • Lord Russell:

“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...

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).”

literal infringement analysis
Literal Infringement Analysis
  • “Applying the Properly Construed Claims to the Accused Product or Process”
  • The question of infringement is a question of fact for a judge/jury.
  • Each and every element must read on the accused device
    • Under literal infringement, in effect, all claim elements were considered to be essential to the invention and thus, the absence of any claimed element resulted in a finding of no literal infringement.
    • It was therefore called an ‘all elements’ test.
  • Infringement:
    • The accused device must perform the identical function required by the claim limitation, and must have identical structureto that disclosed in the specification.
intrinsic e xtrinsic evidence
Intrinsic ------- Extrinsic evidence

“Although we have emphasized the importance of intrinsic evidence in claim construction, we have also authorized district courts to rely on extrinsic evidence, which “consists of all evidence external to the patent and prosecution history, including expert and inventor testimony, dictionaries, and learned treatises.” Markman, 52 F.3d at 980.

intrinsic extrinsic

Claim language


Prosecution History

Papers generated during prosecution


Expert witness testimony

The role of an expert is to assist in putting the Court in the position of a person skilled in the art as of the relevant time.

Intrinsic --------- Extrinsic
literal infringement interactive gift express inc v compuserve inc 1998
Literal Infringement Interactive Gift Express, Inc. v. CompuServe Inc. (1998)
  • Facts:
    • Claims cover system for reproducing information at “point of sale locations”
    • Accused process – sale of software and documents online
  • Issue – is a sale made to a consumer using a computer at home conducted at a “point of sale location”?
literal infringement compuserve case
Literal Infringement – Compuserve Case
  • Analysis
    • Intrinsic evidence evaluated first
      • Look to plain language of claim limitation first
      • If claim language is clear, look to specification and prosecution history only to determine if a deviation from the plain language is required.
      • Do not read limitations appearing in the specification into the claims; specification is used only to help determine what the inventor meant by using the claim terms.
    • Only took to extrinsic evidence to construe claim terms if the claim language remains genuinely ambiguous after considering intrinsic evidence
      • Extrinsic evidence can never be used to vary or contradict the claim terms
    • But extrinsic evidence may always be consulted to assist in understanding the underlying technology.
    • Perspective from which claims are interpreted is the person of ordinary skill in the art.
literal infringement compuserve case1
Literal Infringement – Compuserve Case
  • Analysis
    • Specification defines “point of sale location” as “a location where a consumer goes to purchase material objects embodying predetermined or preselected information.”
    • Court of First Instance: defined this not to exclude a home.
    • Appeal: nothing in the intrinsic evidence excludes a home as a point of sale location.
    • No need for extrinsic evidence
markman hearings
Markman hearings
  • Herbert Markman and Positek Inc. v. Westview Instruments Inc. and Althon Enterprises Inc.(1996),US Supreme Court ruled that
    • “Claim construction is a matter of law that should be decided by a judge alone.”
  • This conclusion paved the way for “Markman hearings” where the judge construes the claims of a patent without any consideration of infringement or validity issues.
  • Claim construction has been done in a pre-trial proceeding called a “Markman hearing”.
balancing tensions the doctrine of equivalents
Balancing Tensions: The Doctrine of Equivalents
  • Ensuring the notice function of a patent
    • “[I]t is only fair (and statutorily required) that competitors be able to ascertain to a reasonable degree the scope of the patentee’s right to exclude.”*


  • Giving a patent owner a fair and reasonable scope of protection

Markman v. Westview, 523 F.3d 967 (Fed. Cir. 1995)

warner jenkinson company v hilton davis chemical co
Warner-Jenkinson Company v. Hilton Davis Chemical Co.
  • The Doctrine of Equivalents
    • Defendant can be liable for patent infringement even though the infringing device or process does not fall within the literal scope of a patent claim.
    • “… [A] product or process that does not literally infringe upon the express terms of a patent claim may nonetheless be found to infringe if there is ‘equivalence’ between the elements of the accused product or process and the claimed elements of the patented invention.”
graver tank manufacturing co v linde air products co 1950
Graver Tank & Manufacturing Co. v. Linde Air Products Co. (1950)
  • Graver test (FUNCTION-WAY-RESULT):
    • It performs substantially the same function
    • In substantially the same way
    • To yield substantially the same result.
  • Graver Tank: “If two devices do the same work in substantially the same way, and accomplish substantially the same result, they are the same, even though they differ in name, form or shape.”
infringement under doctrine of equivalents
Infringement under Doctrine of Equivalents
  • Equitable Doctrine
  • Adheres to literalism yet evolve a doctrine which supplements the claims by extending protection to equivalents.
  • Affords protection to inventions where a product avoids the literal language of the claim by making a noncritical change
  • Each element contained in a patent claim is deemed material to defining the scope of the patented invention
  • Determine if the differences between the elements of the claimed invention and the suspect infringing device or process are “insubstantial”
  • Question of Fact
johnson johnson associates inc v r e service co inc
Johnson & Johnson Associates Inc. v R.E. Service Co. Inc.
  • Facts
    • Claims for printed circuit board with aluminum substrate that protects the thin copper foil
    • Specification states that “other metals, such as stainless steel or nickel alloys, may be used.”
    • Accused devices uses thin sheet of steel as substrate
j j case
J&J Case
  • Issue – can P (J&J) claim the steel substrate by equivalents or was steel substrate dedicated to the public by disclosing in specification but not claiming
  • Analysis
    • Maxwell case (F. Cir.)– subject matter disclosed but not claimed is dedicated to the public domain b/c the patent office does not have an opportunity to review it
    • YBM Magnex case (F. Cir.) – Maxwell is limited to situations where the disclosed but unclaimed matter is distinct from what is claimed; unclaimed equivalents disclosed in the specification are not dedicated to the public domain
j j case1
J&J Case
  • Analysis
    • Infringement analysis proceeds by comparing accused device to the claims, not to preferred embodiments in the specification
    • Disclosure of an embodiment without claiming it dedicates that embodiment to the public domain
      • Contrary rule would encourage narrow claims with broad disclosures to limit the PTO’s role
    • Rader concurrence
      • any foreseeable equivalent should be claimed;
      • equivalents that are unforseeable at the time of the application should be allowed.
uk developments
UK developments
  • UK courts used ‘literal approach’ until the current law entered into force in 1977.
    • Conforming to EPC, Art. 69
  • The courts have recognised that patents must be interpreted purposively.
    • House of Lords 1982 – Catnic v Hill and Smith
    • Lord Diplock – Claims be read through the eyes of the person skilled in the art, and the purpose or function of the invention should be borne in mind when the patent is interpreted.
    • Catnic was confirmed by:Improver Corporation v. Remington Consumer Products Ltd. [1990]
fact of catnic catnic components ltd v hill smith ltd 1982
Fact of CatnicCatnic Components Ltd. v. Hill & Smith Ltd. (1982)
  • Catnic’s patent claimed a lintel (the bar that spans the top of a window to support the weight of the bricks laid above it) having a rear wall member ‘extending vertically’.
  • Hill’s lintel differed from what was illustrated in the Catnic patent in that the rear wall was inclined 6 or 8 degrees off vertical, as shown and highlighted in Figure 4 above. The sloping of the rear wall made the Hill lintels 0.6 to 1.2% weaker in their load bearing capacities than the Catnic lintels.
  • Functionally, it was a negligible difference.

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, being changed or absent, there could be no infringement of the ‘pith and marrow’.
  • The House of Lords overturned and found there to be infringement.
lord diplock purposive c onstruction
Lord Diplock: ‘Purposive Construction’
  • “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"),

A patent specification should be given a purposive construction rather than a purely literal one ...

The question in each case is: whether persons with practical knowledge and experience of the kind of work in which the invention was intended to be used, would understand that strict compliance with a particular descriptive word or phrase appearing in a claim was intended by the patentee to be an essential requirement of the invention so that any variant would fall outside the monopoly claimed, even though it could have no material effect upon the way the invention worked.”


“The question, of course, does not arise where the variant would in fact have a material effect upon the way the invention worked. Nor does it arise unless at the date of publication of the specification it would be obvious to the informed reader that this was so.

Where it is not obvious, in the light of then-existing knowledge, the reader is entitled to assume that the patentee thought at the time of the specification that he had good reason for limiting his monopoly so strictly and had intended to do so, even though subsequent work by him or others in the field of the invention might show the limitation to have been unnecessary.”


“… it 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.

infringement under purposive construction
Infringement under “Purposive” construction
  • Purposive construction is not unique to patent law and has had a long history in contract law and statutory construction.
  • Purposive construction does not ask:
    • "What did the patentee say?" which might be a literal interpretation.
  • Rather:
    • “What was the inventor trying to say?” or
    • "What would a skilled reader have understood the patentee to have been trying to say?”
  • Purposive construction should not allow a patentee to broaden or expand the scope of a claim.
    • It does not ask “What should the patentee have said?”
    • If a patentee failed to claim as broadly as he or she could have, purposive construction should be of no assistance.
  • The last point makes the “Purposive construction” different from the “US Doctrine of Equivalents”.
how the uk purposive construction applies
How the UK purposive construction applies?
  • What would a person skilled in the art have understood the patentee to have used the language of the claim to mean?
uk catnic test lord diplock in catnic
UK (Catnic Test) - Lord Diplock in Catnic

Does the variant have a material effect upon the way the invention works?



Would this have been obvious to a person skilled in the art at the publication date?



Would a person skilled in the art 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?



No Infringement (purposive) infringement

a chair with wheels

Allegedly-infringing products

Claimed invention

A Chair With Wheels













Variant A has no material effect upon the way invention works, but it seems obvious to person skilled – infringement.

The following


A ?

Variant E has material effect upon the way invention works, non-obvious; no strict compliance required – No infringement.

A and E ?

summary uk purposive approach
Summary – UK Purposive approach
  • A patent specification must be read as a whole
  • The description and drawings shall be used to interpret the claims
  • The claims must be interpreted as part of the entire documents
  • The court can hear expert evidence on the meaning of technical terms.
  • The prosecution history (information exchanged between the applicant and the Patent Office during the grant process) can be used to interpret the claims
  • Patent document is read from the point of view of a person skilled in the art and is understood at the time of the priority date.
purposive construction doctrine of equivalents
‘Purposive construction’ ----------- ‘Doctrine of Equivalents’
  • Doctrine of Equivalents protects “substance of the invention”.
  • “Purposive Construction”:
    • Patents protect only the literal meaning of the claims.
    • The patent protects only the invention described in the claims, as understood by a workman skilled in the trade, as of the date of the patent.
    • But the a literal interpretation is based on the construction of ‘the intent of the inventor’ manifested in the patent claims.
    • It does not extend protection to the “substance of the invention”.
contact information
Contact Information