The Difference that Matters: Claim Interpretation vs. Claim Construction in Patent Law

By: Dr. Pallavi Singh and Shashwat Awasthi


To this day, patent infringement suits trouble the courts in so far as the matter relating to the determination of the legal scope of the asserted claims or the claim at issue is concerned. For example, in determining the scope of a claim directed to a “vessel for storing high-pressure gases”, the basic questions that would lie before the deciding body interpreting the claim would be of the following nature: What is the context of the term ‘vessel’? What all did the patentee intend to cover when he/she used the term “high-pressure gases”? Most readers would wonder as to where the difficulty lies in answering the above-mentioned questions as they simply appear to be matters of ordinary linguistic interpretation. However, in reality, the questions are much more complex as they pertain to two related but fundamentally different concepts in patent law – claim construction and claim interpretation.

Not many people are cognisant of the difference between interpreting a patent claim and constructing one. By virtue of the said non-familiarity, some even make the colossal mistake of using the two concepts interchangeably. This article is a brief attempt to highlight the difference between the two concepts, and further, buttress the proposition that this difference is both real and fundamental as argued by leading authorities like Lawrence B. Solum and Tun-Jen Chiang.

To understand the difference between claim construction and claim interpretation, it is important to understand the following concepts which form the very genesis of such distinction:

1) Ambiguity vs. Vagueness

2) Semantic Content of a Text vs. Legal Content of a Text

Ambiguity vs. Vagueness

The two terms are often used interchangeably in day-to-day communication as well as legal discussions. However, in the real sense, there exist deep technical differences between the two. The Oxford English Dictionary defines the term ambiguous as something which is “open to more than one interpretation; not having one obvious meaning”. Therefore, in essence, ‘ambiguity’ signifies multiplicity of meanings. The term ‘light’ is ambiguous because it can mean a variety of things; it can mean the natural agent that stimulates sight and makes things visible, or it can refer to the quality possessed by a substance in terms of weight or colour. Now, in terms of a patent claim, the determination of the correct linguistic meaning of the term ‘light’ would require an analysis of the context in which it was used. This exercise is known as claim interpretation.

On the other side of the spectrum, vagueness is defined as something which “lacks certainty or preciseness in thought or communication”. Therefore, in essence, ‘vagueness’ refers to the existence of borderline cases, i.e., a term is vague if there are cases where there is lack of clarity whether a term might or might not apply. The term ‘light’ in terms of weight is vague. How light must a thing be for it to be considered ‘light’? In terms of a patent claim, the determination of the ambit of the term ‘light’ would require a reading into the intention of the patentee (however, that, as will be explained later, is not exactly useful), the description of the invention as laid out in the specification, extrinsic sources etc. This exercise is known as claim construction.

Semantic Content vs. Legal Content of a Text

Closely connected to the interpretation-construction distinction is another inherent distinction found in almost every legal text, i.e., the distinction between the semantic content of the text and the legal content of the text.

As the name suggests, in a patent claim, semantic content refers to the linguistic meaning of a term in a claim and the consequent meaning attributed to the claim thereby. In contrast, legal content refers to the legal scope of the claim. Coming back to our earlier example of a patent claim directed to a “vessel for storing high-pressure gases”, we can determine the difference between the semantic content and the legal content. The semantic content of the impugned claim would pivot on the linguistic meaning of the term ‘vessel’, in particular, as a vessel may either pertain to a watercraft, a holding container or tube-like structure such as a blood vessel. On the other hand, the legal content of the claim relates to the determination of the legal scope of the term “high-pressure gases” wherein the pressure threshold defining ‘high-pressure’ would have to be determined.

As pointed out by Lawrence B. Solum, interpretation yields semantic content, whereas construction determines legal content or legal effect of a particular text, or in this case, a patent claim.


Claim Interpretation

The distinction between claim interpretation and construction can easily be derived from the preceding paragraphs. Claim interpretation serves the function of determining the linguistic meaning of the terms used in the patent claim by eliminating linguistic ambiguity. However, claim interpretation is not as easy a concept as it sounds and the burning question that usually arises with regards to claim interpretation is: What is the reference point with respect to ‘linguistic meaning’? Does it refer to the ordinary or the literal dictionary definition of the terms or does it refer to how a person skilled in the art would understand the language of the claim?

The jurisprudence in the United States relating to claim interpretation and construction is highly developed and suggests that linguistic meaning refers to how a person skilled in the art would understand the language of the claim because patents assume a readership of the persons skilled in the art or the field of invention. However, few decisions suggest that claims are to be construed according to what the patentee “intended to do.” This standard, however, is prone to circularity because; the courts will interpret claims according to the patentee’s intent, but the patentee’s intent will be to claim whatever the courts allow. Therefore, it follows that a patentee’s intent in this broad sense is a useless point of reference.

Claim Construction

Claim construction is undertaken both during the examination of a patent application in case of an opposition or when a patent is under scrutiny before a court of law where the primary intention of the adjudicating authority is to determine the metes and bounds of a claim. This is useful to understand if the application or the patent is anticipated or obvious in view of prior art or if the invention so claimed has been infringed, as the case may be. Therefore, essentially, the function of claim construction is to determine the legal scope and effect of a patent claim.

Some simple questions with difficult and complex answers have made claim construction a matter of contention between patent practitioners. The questions are: How should claim construction be done? Should intrinsic evidence like description, prosecution history, etc. be given precedence over extrinsic evidence like dictionary meanings, encyclopedias etc.?

A reference to the landmark case of Phillips v. AWH Corp. which deals with the above-mentioned questions is therefore necessary.

The Case of Phillips vs. AWH Corporation 

At issue in Phillips was a patent relating to modular, steel-shell panels that could be welded together to form walls resistant to vandalism, basically meant for prisons, which belonged to Phillips.

The alleged inventive step claimed was that in between these steel walls, internally directed steel ‘baffles’ were placed which would provide bullet-proof capabilities. The alleged infringement of the patent by AWH Corp., a former licensee of Phillips, which developed similar panels without bullet-proof capabilities by virtue of different angle disposition, depended upon the determination of the metes and bounds of the term ‘baffles’. That is, if the claim required the baffles to be disposed at all angles except ninety degrees, then the infringement is not established; if the baffles could be disposed at all angles including ninety degrees, then the infringement is established. Therefore, the question before the Court clearly related to claim construction and not claim interpretation.

The majority in the District Court and the Federal Panel decision held that claim construction analysis should be carried out by placing heavy reliance on patent specification. The minority, however, stipulated that extrinsic evidence such as the ordinary dictionary meaning should be given primary importance. The Federal Circuit in its en banc decision, deviating from the principles laid down in Texas Digital Systems, Inc., held that “…the patent specification is intended to support and inform the claims. It is in the interests of a sound patent system and inventors, as well as the public, to hold inventors to their disclosures”. Hence, the Court emphasised that intrinsic evidence like specification, prosecution history, etc. should be given precedence over extrinsic evidence like dictionaries, encyclopedias etc.

Recently, the USPTO administered regulations which would require the Patent Trial and Appeal Board (hereinafter ‘PTAB’) to apply the standard set in Phillips in claim construction cases in order to avoid different claim construction standards being applied by the PTAB and the District Courts. The PTAB used to apply the broadest reasonable interpretation standard prior to the coming of the said regulations.

However, the Phillips decision is far from being perfect and is till date a subject matter of debate between patent practitioners. The debate regarding the methods of claim construction is far from over. Some practitioners advocate the precedence of extrinsic evidence over intrinsic evidence arguing the use of specification at a later stage only to the extent of verifying disclaimers against their ordinary meaning. Other eminent authorities like Professors R. Polk Wagner and Joseph Scott Miller argue that intrinsic evidence should control claim construction only if it is unambiguous and specific. But that is not all. The most unfortunate aspect of the Phillips decision is that the Court did not apply the above-mentioned principle, i.e., the precedence of intrinsic evidence over extrinsic evidence, to the facts of the Phillips case.


Patents are arguably the most important intellectual property, economically as well as scientifically. In that regard, patent claims serve an essential function of determining the extent of the patentee’s monopoly. It is therefore important for every individual associated with patent law to realise the difference between interpreting patent claims and constructing patent claims. There is little but voluminous work on the concept, and in that light, the article aims to have accomplished the task of briefly explaining the difference between the two concepts using real-life examples. There are, however, many questions related to these concepts which remain to be answered; for example: What is the most efficient way to construct a patent claim? Should interpretation always precede construction?

Dr. Pallavi is a senior associate at Intll Advocare, New Delhi while Shashwat is currently a law undergraduate at Dr. Ram Manohar Lohiya National Law University, Lucknow.)

One thought on “The Difference that Matters: Claim Interpretation vs. Claim Construction in Patent Law

  1. Claim construction and Claim interpretation. Imagine for a moment we remove the word “Claim”. Then it becomes construction and interpretation. The example given is a “Vessel” for storage of “high pressure Gas”. High pressure gas Is normally considered as compressed gas above 10kg per cm square in normal temperature and a vessel which can store such compressed gas is called “High pressure vessel”.The material of storage can be in gaseous or liquified state. For the purpose of interpretation various other parameters are generally considered:is it only for storage or for transportation or for both, what is permissible range of temperature during storage/transportation, what is the degree of Safety levels needed etc etc. Can I venture to say construction should be viewed wrt design of the vessel, selection and material used, process of construction, testing and process ofquality control etc.Interpretation should be with reference to parameters of Liquid/gas, presuure to withstand, temperatures(could be extremely hot (+) or extremely cold (-), duration of storage/transportation, safety levels required, last but not the least optimum cost etc. Construction may be viewed as “basic and fundamental research” whereas interpretation be”Application/Applied research “.. I don’t know when we tag” CLAIM”to construction and interpretation, whether what I conveyed has. some sense/meaning on the subject.

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