Patent Drafting: Employing Claim Differentiation to Ensure Broad Construction

EDITOR’S NOTE: This article is an excerpt from Rules of Patent Drafting: Guidance from Federal Circuit Cases, 2014 Edition, which is now available at This is the fifth installment of the series. To read other installments please see Joseph Root on Patent Claim Drafting.


PrintThe most significant obstacle to achieving patent breadth in contemporary patent law lies in the Federal Circuit’s proclivity to import imitations from the specification into the claims. The Court justifies its actions as merely discerning the inventor’s intent to limit the invention. The most effective counter to that activity is claim differentiation—the concept that claims are presumed to have different meanings, so a limitation expressly present in one claim should not be read into another claim, particularly where the narrower claim is dependent upon the broader. The Federal Circuit’s formulation of that rule was well stated in SRI Int’l v. Matsushita Elec. Corp.: “It is settled law that when a patent claim does not contain a certain limitation and another claim does, that limitation cannot be read into the former claim in determining either validity or infringement.”

Courts often express this principle in terms of avoiding claim redundancy. The Phillips court faced that question in dealing with steel-shell panels that can be welded together to form vandalism-resistant walls. The broadest claim included a limitation “internal steel baffles extending inwardly from the steel shell walls.” The court was required to determine exactly what characteristics were implicit in the term “baffles,” and one technique employed for that purpose was an examination of the other claims. For example, dependent Claim 6 recited, “the internal baffles of both outer panel sections overlap and interlock at angles providing deflector panels extending from one end of the module to the other.” “If the baffles recited in claim 1 were inherently placed at specific angles,” the court reasoned, “claim 6 would be redundant.” Thus, a construction of Claim 1 that included a specific angle would be improper, based on the doctrine of claim differentiation.

To bring this principle to bear on the problem of claim breadth, consider a patent disclosing only a single embodiment, with a main claim whose scope extends beyond that of the embodiment (yet inside the ambit of any cited prior art). As discussed at length elsewhere, without diverse claims, courts are likely to determine that the embodiment does not simply illustrate the invention; it is the invention. The court then follows promptly by reading limitations of the embodiment into the claims.

That issue appears in nCube Corp. v. SeaChange Int’l, Inc., where the technology addressed data storage and retrieval in a networked environment. Claim 1 was broadly drawn, and it included, “an upstream manager receiving messages from said client and routing said messages to an appropriate service on said server, said upstream manager being coupled to a first network.” The specification set out only one embodiment. The embodiment employed logical addressing to send messages, with the upstream manager using the logical address to establish a unique “virtual circuit” for connection with an individual client. Claim 1 speaks only of “routing said messages,” without specifying logical or physical addresses, and the accused infringer argued that Claim 1 should be limited to logical addressing, because that process is the only one set out in the embodiment. In light of results in similar situations, one must ascribe at least a high likelihood that the logical addressing limitation would have been read into the claim, but for one fact: Dependent Claim 2 specifically recites the “virtual circuit” limitation, and dependent Claim 4 adds logical addressing. Thus, limiting claim 1 to logical addressing “would impermissibly read the ‘virtual connection’ limitation of claim 2 into claim 1, making these claims redundant.”

Claim differentiation is a powerful weapon. Carefully used, it can completely block the importation of limitations from an embodiment. Drafters should store this tool within easy reach, and in any situation where the scope of a main claim exceeds the literal scope of the broadest embodiment, claims should be inventoried to ensure that every limitation present in the embodiment but not in the claim is or becomes the subject of a dependent claim.



Varying class

The doctrine of claim differentiation generally addresses the specific effect of having claims that differ in some respect; that is, the claims in question stand apart, each having its own independent scope. This doctrine says nothing, however, about any particular advantages or effects of specific claim differences. Analysis, ;however, reveals that two primary differences can be identified— claims of varying class and varying scope.

As a matter of good drafting practice, apart from considerations of validity before the Federal Circuit, drafting claims in various statutory classes should be a practitioner’s general rule. Providing claims of varying statutory class allows the drafter to present claims of content ranging from the purely functional to the purely structural, confident that claim differentiation will maintain the line between these claims.

The result is illustrated in DSW, Inc. v. Shoe Pavilion, Inc., concerning a patent directed to a system and method for storing and displaying a large stock of footwear for customer self-service. The litigation addressed six claims: three concerned methods for displaying and storing footwear, and three were directed to apparatus. Regarding the display and storage of footwear, one claim recited a footwear display and stack divider module; a second addressed a system for displaying and storing footwear; and a third claimed a cabinet for displaying and storing footwear. Each of the apparatus claims included a “track and roller assembly,” recited as a component of a support module. The method claims each included a “generally vertically disposed, horizontally movable positionable stack provider,” recited in that fashion in the independent claim and including additional detail in each dependent claim. No method claim included a “track and roller assembly.”

Nonetheless, the district court imported the “track and roller assembly” limitation into the method claims. The Federal Circuit reversed that construction, characterizing the method claims as being broad but not ambiguous. The court set out the applicable rule, quoting from an earlier decision:

[T]his court has consistently adhered to the proposition that courts cannot alter what the patentee has chosen to claim as his invention, that limitations appearing in the specification will not be read into claims, and that interpreting what is meant by a word in a claim “is not to be confused with adding an extraneous limitation appearing in the specification, which is improper.”[1]

Note that the drafter here achieved several objectives. First, the details of the “track and roller assembly” were set out in several different contexts. To the extent that this limitation might be successful in overcoming a prior art reference, the drafter gave herself several avenues through which to accomplish this objective. Further, a broadened form of the same assembly, recharacterized as a “horizontally movable positionable stack divider,” was combined with the method claims, providing an entirely different angle from which to approach patentability.


Varying scope

Within a single statutory class, claim differentiation is most easily achieved by varying claim scope. A broad independent claim, with narrower dependent claims, not only maximizes the probability of obtaining optimum infringement coverage, but it also increases the chances of achieving a desired claim construction. Additionally, the content of the dependent claims often can help define the contours of the parent claim.

A typical example can be seen in Finisar v. DirectTV Group, where the patent concerned broadcasting audio and video programs to consumers. The claimed process called for filtering a data stream carrying media content to identify a specified set of data packets containing content selected by a user. That step was followed by “downloading into a memory storage device those of said received data packets which match said specified set of requested data packets.” The claim construction turned on whether the method required storage of the downloaded data or whether the simple act of downloading constituted sufficient response to the claim term. The district court had construed the term to mean “the data filter transfers into a memory storage device the data packets specified in the filter data,” without requiring storage of the data for later availability.

The court looked to a dependent claim, which modified the downloading step. There, the recitation included “temporarily storing received data packets in a buffer” and “forwarding those data packets in said buffer” to a “predefined destination.” The fact that both a buffer and a “predefined destination” were specifically mentioned, the court reasoned, indicated that buffer could not be the “memory storage device” of the parent claim. Further, the goal of the invention, allowing consumers to view media content on demand, would not be served unless the data were stored for some time. Thus, downloading was construed as “transferring the desired data into a device capable of saving it for later access.”

In a case involving shipping containers, where the main claim addressed a storage structure “coupled to” a container, the court construed that coupling as restricted to direct, rather than indirect, attachment, leading to judgment of non-infringement. The Federal Circuit looked to the dependent claims, however, and noted that a dependent claim recited an indirect attachment. In light of that fact, the court said, “the scope of independent claim 1 is presumed to be broader to allow for other types of indirect attachments.” The claim construction was broadened accordingly. A similar result obtained regarding eyeglasses, where an independent claim recited “a magnetic member”, which the accused infringer argued should be limited to a permanent magnet. Because a dependent claim specifically limited the “magnetic member” to “magnet,” the court agreed with the broad reading.

One can and should employ claims of varying scope to accomplish the straightforward goal of varying the scope of coverage. The suggestion here goes beyond that goal, by employing the narrow claims to preserve the broad claims. In a sense, that process turns claim drafting on its head, but the Disclosure Revolution can do that.


Beware of exceptions

In most circumstances, claim drafting gets by with a little help from its friends, but there are limits. Occasionally, claim differentiation runs into Disclosure World, butts heads, and loses. A noted example, featuring vigorous disagreement between Chief Judge Rader in the differentiation corner, and Judges Lourie and Plager, occurred in Retractable Technologies, Inc. v. Becton, Dickinson and Co. The technology concerned retractable syringes, in which the needle retracts into the syringe body after use. The disputed claim construction centered on whether the syringe body necessarily was formed in a single unit or from multiple elements. The independent claim recited, “[a] syringe comprising a hollow body.” A dependent claim followed, calling for “[t]he syringe of claim 1 comprising a one-piece barrel.” Classic claim differentiation, Chief Judge Rader maintained, calling for a broad independent claim. Judge Lourie’s opinion invoked Phillips to focus on the specification, where the syringe was repeatedly described as having a one-piece body, in both the Detailed Description and the Summary. The Background distinguishes the claimed invention from the prior art on the basis of a one-piece body, and the drawings show only a one-piece construction. Taking account of all this description, Judge Lourie concluded that “a construction of ‘body’ that limits the term to a one-piece body is required to tether the claims to what the specifications indicate the inventor actually invented.” Chief Judge Rader responds with reasoning straight from the classical world of claim dominance:

When the inventor intended to impose a one-piece structural limitation, he did so explicitly, as shown by dependent claims 14 and 57 in the ‘224 patent. Consequently, this court should not impose such a structural limitation on claims that merely use the term “body” without a “one-piece” modifier. Such a construction is contrary to the ordinary and customary meaning of the word “body,” violates the doctrine of claim differentiation, and lacks support in the patents at issue.

Claim differentiation is an excellent weapon, but some days Disclosure World wins.



Warning & Disclaimer: The pages, articles and comments on do not constitute legal advice, nor do they create any attorney-client relationship. The articles published express the personal opinion and views of the author as of the time of publication and should not be attributed to the author’s employer, clients or the sponsors of

Join the Discussion

One comment so far.

  • [Avatar for Ken]
    September 17, 2014 06:59 pm

    “…to tether the claims to what the specifications indicate…”

    The problem with their ruling here was that originally filed claims are PART of the specification, so unless there was a problem with enablement or prior art, the claim set itself provided written description support for the absence of that limitation – in the sense that the dependent claim containing that limitation was a clearly implicit way of saying that the base claim lacked that limitation.