A Means-Plus-Function Trap—Presumption Fails to Save Functional Claims Lacking Structural Antecedent
Updated: Oct 17
. . . “This is the epitome of functional claiming: a black box that captures any and all structures that fulfill the function, just as if ‘means’ was used.”
In WSOU Investments LLC v. Google LLC, No. 2022-1064 (Fed. Cir. Oct. 6, 2023), the United States Court of Appeals for the Federal Circuit (“Federal Circuit”) rejected an appeal by WSOU Investments LLC (“WSOU”) from a final judgment of invalidity of its U.S. Patent 8,751,585 (“the ’585 patent”) by the United States District Court for the Western District of Texas. The district court had determined that (1) the asserted claims in the patent are means-plus-function claims even though the claims do not expressly include the word “means” and (2) the claims are indefinite because certain claim limitations lacked sufficient corresponding structure in the patent’s specification even though the term “processor” is recited as a claim limitation.
The ’585 patent is directed to a method for managing electronic messages in a user’s inbox within a communication system. The method involves filtering electronic messages using user-created archiving rules that respond to the actions taken by the user in response to the message.
The claimed communication system comprises an electronic message client that allows a user to manage the electronic messages in the inbox. The client utilizes four types of “processors,” including: (1) a client management processor that enables the user to select a message, assign an archiving rule to it, and define an archive location within the communication system where the message should be moved after a specified action is detected; (2) a detection processor that identifies when the specified action has been carried out; (3) an event management processor that generates a command to move the message to the archive location; and (4) a collaborative application management processor that is responsible for managing collaborative applications within the broader communication system.
The appeal in this case concerned the fourth “processor” limitation and the district court’s construction of “a collaborative application management processor configured to manage collaborative applications” as a means-plus-function limitation.
In its appeal, WSOU argued that the district court erred procedurally by not expressly addressing the rebuttable presumption against construing a claim as a means-plus-function claim when the word “means” is not used in the claim. See Williamson v. Citrix Online, LLC, 792 F.3d 1339, 1349 (Fed. Cir. 2015) (en banc in applicable part). According to WSOU, the district court was obliged to affirmatively find that the presumption had been overcome—which it did not do in its written decision. In response, the Federal Circuit said that it was “unaware” of any requirement that the district court “expressly state that the exception was overcome” and emphasized that “WSOU cites no authority to support that proposition.” Opinion at 8.
According to the Federal Circuit, it was enough for the district court to explain its rationale for construing the claims as means-plus-functions claims. Id. The district court reached that conclusion because the disputed “claim term fails to recite sufficiently definite structure or else recites function without reciting sufficient structure for performing that function.” Id. In the district court’s view, the claim term “processor,” standing alone, did not impart structure to the claims’ limitations, prompting the district court to conclude that “in this case, the claimed processor limitation was written in means-plus-function form because nothing in the claim or the specification describes structure.” Id. (emphasis in original). The Federal Circuit agreed. Id.
The Federal Circuit also agreed with the district court that there is no “categorical rule” on whether the claim term “processor” is structural or functional. Id. at 9. Determining whether “processor” is structural or functional requires “look[ing] to the case-specific record here to determine whether the phrase ‘collaborative application management processor configured to manage collaborative applications’ is ‘understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure.’” Id. (quoting Williamson, 792 F.3d at 1349). The Federal Circuit agreed with the district court that nothing in the record suggests that “processor” is used in the patent as a structural term.
The Federal Circuit likewise agreed with Google that the term “processor” is instead used in the claims as a generic equivalent to “means” and that the terms “configured to manage collaborative applications” and “collaborative application management processor” did not provide structure but only described the overarching functions of an “undefined and uncertain” “processor.” Id. In answer to the question, “What structures will the claim limitation read on?”, the Federal Circuit rejoined, “Any that fulfill the function of managing collaborative applications.” Id. at 9-10. According to the Federal Circuit, “This is the epitome of functional claiming: a black box that captures any and all structures that fulfill the function, just as if ‘means’ was used.” Id. at 10. The primary fault of the claims was their lack of any “indication of how the processor manages collaborative applications” and their failure to “describe how this processor interacts with the other claimed components in a way that might inform the structural character of the limitation.” Id.
Turning to the patent’s specification, the Federal Circuit noted that the patent nowhere discusses either a “collaborative application management processor” or a “processor configured to manage collaborative applications.” Id. Indeed, the term “processor” is not discussed at all in the patent’s specification. Id. Instead, the patent specification conspicuously discusses only a “collaborative application management means.” Id. (emphasis in original). Moreover, during prosecution of the patent’s application, WSOU changed the original as-filed claim language “means for management of collaborative applications” to “a collaborative application management processor configured to manage collaborative applications.” Id. at 12 (emphasis added). The Federal Circuit explained that the amendment was unavailing and that a “patentee cannot avoid a means-plus-function construction by merely replacing the term “means” in the claims with other, equally functional language.” Id.
Having determined that the district court had properly construed the patent claims as means-plus-function claims, the Federal Circuit next considered whether Google had proven by clear and convincing evidence that the claims are indefinite due to a lack of corresponding structure in the patent’s specification that is clearly linked to the claimed function. See Williamson, 792 F.3d at 1351 (adequate corresponding structure); Triton Tech. of Tex., LLC v. Nintendo of Am., Inc., 753 F.3d 1375, 1378 (Fed. Cir. 2014) (clear link between claimed function and corresponding structure). Regarding the claimed function, both parties agreed that the function of “collaborative application management processor” means “managing collaborative applications.” Opinion at 13.
For the following reasons, however, the Federal Circuit concurred with Google that the specification fails to disclose sufficient structure that performs the function of “managing collaborative applications.” First, the specification does not actually discuss or describe the claim term “collaborative application management processor.” Id. at 14. Second, the specification lacks any disclosure of an algorithm directing the function of “managing collaborative applications” and thereby imparting specific structure to the claimed “processor.” Id.; see Alfred E. Mann Found. for Sci. Res. v. Cochlear Corp., 841 F.3d 1334, 1342 (Fed. Cir. 2016) (algorithm required as supporting structure for “a general purpose computer or microprocessor” to “prevent pure functional claiming”). Finally, although WSOU pointed to “databases” disclosed in the specification as corresponding structure, the specification only described the databases functionally, not structurally, as “means for managing collaborative applications” that “enable the recording and storing of data.” Id. (emphasis in original). That limited description of the databases, therefore, explains neither how the databases “manage collaborative applications” nor how they serve as an algorithm for executing the claimed function. Id. at 15.
The Federal Circuit, therefore, affirmed the district court’s judgment that the patent claims were indefinite because the term “collaborative application management processor” lacked a sufficient description in the patent’s specification of the structure corresponding to its function. Perhaps the most surprising aspect of this case is the patent’s use of specific claim language such as “collaborative application management processor” that has no antecedent in the patent’s specification. It is as if the patent’s claims were drafted in isolation from the patent’s written description of the invention.
Understandably, patentees prefer broad claims, and functional language often provides broad claim scope. This case, however, demonstrates the risk that such claims can be construed as means-plus-function claims despite the judicial presumption against such an interpretation in the absence of the claim term “means.” This case further shows that including putatively structural terms such as “processor” in an otherwise functional claim may not save the claim from a means-plus-function construction—especially where there is no clear structural antecedent for the term in the patent’s specification. The lessons drawn here suggest that patent practitioners should exercise caution in drafting claims that rely on functional claim limitations in the absence of unambiguously structural limitations and likewise should confirm that the patent’s specification provides structural written description in support of the claimed functions to ensure the claims’ validity and enforceability against third parties.