The Rosetta Stone for the doctrine of means-plus-function patent claims.

AuthorHofmann, Rudolph P., Jr.

    A patent grants to inventors "`the right to exclude others from making, using, offering for sale, selling, or importing the patented invention' in exchange for full disclosure of the invention."(1) The patent must contain a complete description of the invention in sufficient detail so that a person skilled in the art to which the invention pertains can practice the invention.(2) The patent must conclude with one or more claims which particularly point out and distinctly claim the subject matter that the patentee regards as the invention.(3)

    The claim measures the scope of the patent grant.(4) Patent in fringement generally is established if the elements or limitations of the claim are found in an accused device, or, in other words, if the claim "covers" the accused device.(5) A claim is invalid or unpatentable if it is overbroad, indefinite, or if it covers the prior art. For over a century, inventors have been required to specify with particularity the claimed invention so that the inventor might be secured all of which she is entitled, the public might be apprised of what conduct is prohibited during the patent term, and the invention might be defined for purposes of determining whether it is patentable.(6)

    Federal patent power derives from the United States Constitution which authorizes Congress "[t]o promote the Progress of Science and useful Arts by securing for limited Times to ... Inventors the exclusive Right to their respective Discoveries."(7) Since 1790, Congress has exercised this power and has periodically enacted and amended various patent statutes.(8) The last major revision of the patent statutes, and also the first major revision since 1870, is the 1952 Patent Act which introduced into law Title 35 of the United States Code.(9) The Act's acclaimed purpose was to revise and codify the existing laws relating to patents and the Patent Office.(10)

    The 1952 Patent Act appended as the last paragraph of section 112 new language relating to functional claims, i.e., claims that define an invention in terms of what it does rather than in terms of what it is. Unmodified since it was first enacted, this paragraph provides:

    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

    claim shall be construed to cover the corresponding structure,

    material r or acts described in the specification and equivalents


    The first clause permits a patent applicant to express an element in a combination claim in terms of what it does rather than in terms of its structure.(12) The second, or scope clause, defines the scope of means-plus-function language and specifies the breadth of protection otherwise permitted by the first clause.(13) In the specification, the applicant must disclose the structure, materials, or acts that perform the claimed function; the means-plus-function limitation in the specification must be construed to cover the structure, material, or acts and their equivalents.(14) Thus, while general claims enjoy a scope as broad as their unambiguous claim language permits, means-plus-function claims are given a different, more limited treatment.(15)

    Combination claims with elements described in terms of what they do have long been recognized as apt.(16) Such claims provide an inventor with flexibility to claim what she regards as the invention. Terms that define what the element does may provide a way to claim the invention in cases where structural terms are unnecessarily cumbersome or inadequate. Also, the broad coverage afforded by functional terms allows the courts to resolve infringement issues without extending patent protection beyond the scope of the literal claim.(17) Section 112, last paragraph, provides a vehicle for such claims and for the realization of these benefits.

    1. The Difficulties of Means-Plus-Function Limitations

      One might suspect that over forty years of precedent(18) would have resolved means-plus-function issues implicated under section 112, last paragraph. Unfortunately, little could be further from the truth. The last paragraph (the scope clause in particular) has presented its share of interpretative and logical difficulties, extending from the scope and definiteness of means-plus-function limitations to the application of the statute itself. The resolutions to these difficulties have serious and often dispositive consequences.

      In a recent case, Valmont Industries, Inc. v. Reinke Manufacturing Co,(19) a Federal Circuit panel held ipse dixit that, in respect to. section 112, last paragraph, an "equivalent results from an insubstantial change that adds nothing of significance to the structure, material or acts disclosed in the patent specification."(20) To define equivalents, the court merely borrowed from contemporary doctrine of equivalents analysis(21) which broadens the scope of protection from the literal language of the claim(22) and serves a different purpose altogether.(23) Such a constricted definition of scope under the statute casts considerable doubt as to the utility of means-plus-function patent claims for protecting an invention, because the scope of enablement (generally related to the permissible scope of protection) often extends well beyond insubstantial changes to the disclosed embodiments.(24) A single embodiment, once imagined, often can provide broad enablement, since other embodiments can then be made without difficulty.(25) Although at the time of making an application for patent only one device may be known that embodies the invention, other embodiments or improvements may later become available.(26) In such cases, if protection is not extended to such embodiments, then the inventor is cheated out of a fair scope of the invention.(27)

      Section 112, last paragraph, essentially provides a statutory exception to the general requirement that the claims provide notice to all of the proper scope of patent protection.(28) For example, there is no legally defined limit as to the extent to which structure, material, or acts described in the specification should correspond with a means-plus-function limitation.(29) This makes the claim indefinite: applicants and patentees can argue that a given claim should be construed to cover one set of "corresponding" structures in order to avoid the prior art, while accused infringers can argue another set to avoid infringement.(30) Also, the determination of what constitutes an equivalent has long been mired with ambiguity and uncertainty.(31) The courts are unable to provide meaningful guidance for determining when changes to the disclosed embodiments are "insubstantial," leaving uncertain what qualifies as an equivalent within the meaning of the statute.(32) The determination of claim meaning and scope thus depends upon the sympathies and prejudices of any one of the hundreds of federal judges that patentees and accused infringers may find themselves before at some unknown time in the future.(33)

      The last paragraph was also the subject of a protracted struggle between the Federal Circuit and the Patent Office over the proper application of the statute in determinations of patentability.(34) The Patent Office sought to avoid, in determining claim scope in the ex parte context, the kind of troublesome equivalency analysis required of the courts in determinations of infringement.(35) In In re Donaldson Co.,(36) a unanimous Federal Circuit sitting in banc held that [sections] 112 applies to means-plus-function language regardless of the context in which it arises, be it as part of a patentability determination in the Patent Office or as part of a validity or infringement determination in a court.(37) Since the United States Patent and Trademark Office ("PTO") now must render patentability determinations by referring to the scope clause to construe claims, the applicant arguably need not amend into the claim the structure, material, or acts to distinguish it from the prior art. The PTO contends that it now is possible to define a separate, patentable invention, even if the claim covers the prior art or contains the same literal wording of a claim in another application or patent.(38) Such claims are indefinite in that they fail to define what the applicant regards as the invention, and they cannot properly form the basis of an examination or determination of validity.

      The problems of indefiniteness and proper scope are exacerbated by a lack of clear guidance as to what constitutes a means-plus-function limitation to trigger application of the last paragraph. Whether the last paragraph applies to a given claim is critical and often dispositive, because the scope of the claim under the last paragraph is less than that under general claim construction principles.(39) The question of whether the last paragraph applies to a means-plus-function limitation is implicated when the statement of function recites some structure. The issue has been resolved by considering both the use of structural language in connection to the statement of function,(40) and the degree of structure recited in the claim.(41) However, reasonable minds differ as to how much structural recitation will or will not trigger the application of the last paragraph.(42) Further, there are conflicting Federal Circuit panel decisions regarding the necessary proofs for degree of structure, and whether the use of the term "means" creates a presumption that the last paragraph applies to a given limitation.(43)

      No question is more basic or more common in patent law than the scope of patent protection. The last paragraph provides uncertainty as to the construction of a means-plus-function limitation. Such uncertainty has detrimental consequences. For example, the uncertainty of the meaning and scope of a means-plus-function limitation makes difficult the assessment of likely outcomes of patent...

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