The changing meaning of patent claim terms.

• Author: Lemley, Mark A.

TABLE OF CONTENTS I. PRINCIPLES OF CLAIM CONSTRUCTION A. Situating the Meaning of Claim Terms in Time 1. Novelty and Nonobviousness 2. Enablement and Written Description 3. Means-Plus-Function Claims 4. Infringement B. Defining Patent Claims Consistently II. CHOOSING BETWEEN THE APPROACHES A. Justifying Unified Claim Construction B. Selecting a Time for Determining Claim Meaning C. The Scope of Patents Under a Filing-Date Standard III. CONCLUSION Dictionaries are word museums. Like archaeologists at a dig, lexicographers mine the language through the eons for patterns of usage. Language evolves, and yesterday's meaning may disguise today's nuance. (1)

The claims of a patent are central to virtually every aspect of patent law. The claims define the scope of the invention, and their meaning therefore determines both whether a defendant's product infringes a patent and whether the patent is valid. One of the most significant aspects of patent litigation is "claim construction," the process of defining the words of the claim in other, theoretically clearer words. (2) Courts construe the claims of the patent by starting with the plain meaning of their terms as they would be understood by a person having ordinary skill in the art, or PHOSITA. Claim construction occurs in every patent case during a "Markman hearing." (3) Indeed, claim construction is so important to patent litigation that once the court construes the claims, most patent cases settle, (4) and those that do not are often decided on summary judgment. (5) As Judge Rich succinctly put it, "the name of the game is the claim." (6)

In order to construe the claims of a patent, the court must fix the meaning of the claim terms as of a particular point in time. Both the knowledge of the PHOSITA in a particular field and the meaning of particular terms to that PHOSITA will frequently change over time. (7) Indeed, the risk of change in the meaning of terms over time is particularly great in patent law, because patents necessarily involve new ideas, and the process of assigning terms to describe those new ideas is not static. As the Supreme Court recognized many years ago, "it does not follow that when a newly invented or discovered thing is called by some familiar word, which comes nearest to expressing the new idea, that the thing so styled is really the thing formerly meant by the familiar word." (8) In that case, the Court found that the meaning of the term "bridge" in a 1790 statute did not mean the same thing in 1860 after the development of railroad bridges. The term was the same, but its scope had changed over time in response to changes in technology.

But at which point in time shall we fix the meaning of the claims? It is a fundamental principle of patent law that the time as of which we determine the meaning of claim terms varies depending on what legal rule is at issue. Where the question is one of novelty or nonobviousness--whether the invention is truly new--the courts compare the patented invention to the prior art as both were understood at the time of the invention. Where the question is one of enablement or written description--whether the inventor understood and described the invention in sufficient detail--courts evaluate the adequacy of the disclosure based on the meaning of the claims at the time the patent application was filed. Where the question involves the meaning of a special patent claim element called a "means-plus-function" claim, courts evaluate the scope of that claim element at the time the patent issues. And where the question involves alleged infringement of the patent, courts evaluate infringement in at least some circumstances based on the meaning of the claim at the time of infringement. What claim terms would mean to one of ordinary skill in the art therefore may depend on what legal rule is at issue, and therefore the time as of which we ask the question.

An equally fundamental principle of patent law is that patent claims must be construed as an integrated whole. A patent claim may not be treated "like a nose of wax which may be turned and twisted in any direction, by merely referring to the specification, so as to make it include something more than, or something different from, what its words express." (9) In particular, patentees (or accused infringers, for that matter) are not permitted to argue that a patent claim means one thing when it comes to validity and something else entirely when it comes to infringement. Instead, courts give claims a single meaning in any given case, engaging in only one act of claim construction for any given patent. Under this principle, patent claim terms have a single definite meaning. In part this is a matter of fundamental fairness--a sense that what's sauce for the goose is sauce for the gander. But it is also necessary if a patent is to put the public on notice of what the patentee owns.

These two principles contradict each other. The meaning of technological terms is fluid. A term that means one thing to scientists at one time may mean something different later as understanding in the field increases. Because both patent prosecution and patent litigation can take years and even decades, (10) fixing the time at which we determine the meaning of any given term may turn out to matter in a substantial number of cases. When the meaning of a patent claim term changes over time, the first principle would give that term a different meaning for validity purposes than for infringement purposes. But in doing so, the court would undermine the second principle, since the claim term will not mean the same thing for all purposes, and it may indeed be impossible to determine the scope of a patent at all on an ex ante basis.

This tension has been latent for some time, but it came to a head in Superguide Corp. v. DirecTV Enterprises. (11) In that case, the question was whether a 1985 patent application that used the claim term "regularly received television signal" could be construed to cover digital television signals that were not developed until well after the patent issued. The Federal Circuit held that it could, relying on the well-established principle that the meaning of the claim term for infringement purposes was determined as of the time of infringement, not the earlier filing date. Judge Michel dissented. He started with the assumption that the meaning of the claims was fixed as of 1985, and concluded that the claim language in question would not have been understood in 1985 to cover digital television. Both the majority and the dissent are correct within their own spheres; their disagreement comes from the fact that they start from fundamentally different principles. Other cases have presented the same problem. (12)

In Part I of this paper, I document the distinguished pedigree of both principles. In Part II, I argue that patent claim terms should have a fixed meaning throughout time and that this meaning should be fixed at the time the patent application is first filed. Part II also discusses some complications that arise as a result of the prosecution process and how to deal with the problem of later-developed technology.

1. PRINCIPLES OF CLAIM CONSTRUCTION

   1. Situating the Meaning of Claim Terms in Time

   Claim construction is a versatile creature, underlying virtually every doctrine in patent law. The role of claim construction is always to define the scope of the claims, though the reasons we want to define that scope differ depending on the legal rule in question. In this Section, I discuss the most common cases in which claim construction affects substantive patent determinations of validity or infringement. In each case, the application of the legal principle is bound up with the understanding of a hypothetical person having ordinary skill in the art, or PHOSITA. (13) The role of the PHOSITA is significant for our purposes, because the meaning of claim terms is also determined by asking what the PHOSITA would understand them to mean. (14) There is a natural and understandable tendency to define the PHOSITA for claim construction purposes as the same person with the same knowledge as the PHOSITA for validity and infringement purposes, though that may in fact be an error. (15)

   1. Novelty and Nonobviousness

      In order to decide whether a patented invention is novel and nonobvious, we must know what the patent covers, because a patent covering a range of devices or chemicals will be held invalid if even a single one of those covered devices exists in the prior art. (16) Whether the device exists in the prior art for novelty purposes is determined by reading the relevant references to determine whether the PHOSITA would have understood that the references taught the claimed invention. (17) Whether an invention is obvious is determined by asking whether the PHOSITA would have found the differences between the prior art and the claimed invention obvious." (18) Novelty and nonobviousness are both determined as of the date of invention. (19) Because novelty and nonobviousness both focus on what the PHOSITA would understand from the prior art at the time the invention was made, it seems to make sense that the meaning of claim terms should also be determined as of the date of invention. And indeed the Federal Circuit has held in the context of [subsection] 102 and 103 that "claims are to be given their ordinary and objective meaning as of the time of the invention." (20)

   2. Enablement and Written Description

      In order to decide whether a patentee has sufficiently disclosed and described her invention, we must know what the patent covers, because the statute requires the patent to enable one of ordinary skill in the art to make and use the full range of the claimed invention, (21) and the court has construed the written description doctrine to require proof that the patentee possessed the full range of the claimed invention. (22) Without knowing how broad the patent is, a court can't...