The recent en banc opinion in Williamson v. Citrix (Fed. Cir. 2015) highlights the dangers of functional claiming in computer-implemented inventions. On June 16, 2015, the Federal Circuit decided en banc to overrule precedent that characterizes as “strong” the presumption that that a limitation lacking the word “means” is not subject to § 112(f). 
Applying a different standard, which is discussed below, the court found the term “distributed learning control module” is subject to § 112(f) and is invalid as indefinite under § 112(b). Just under a year ago in November 2014, the court, in Williamson v. Citrix, reached the opposite conclusion with respect to whether the claim term invoked § 112(f).
Recent CAFC decisions have also touched on the dangers involved with using functional claim limitations. In EON Corp v. AT&T (Fed. Cir. 2015), the CAFC affirmed invalidity based on indefiniteness for failing to disclose software algorithms corresponding to means-plus-function language. In Robert Bosch, LLC v. Snap-On Inc. (Fed. Cir. 2014), the court affirmed claim limitations as indefinite after determining that the claims invoke 35 U.S.C. § 112(f), even though the phrase “means” was not explicitly recited in the claims.
Functional claim language is increasingly being used by practitioners to capture the metes and bounds of an invention, especially in computer-implemented inventions. Sometimes using functional language in a claim limitation is unavoidable. There is nothing inherently wrong with defining some part of an invention in functional terms; however, using functional claim language carries some risks. Therefore, it’s important to understand how functional language is interpreted by reviewing authorities, such as the PTAB and CAFC, and the possible consequences of using functional language in a claim. The risks surrounding functional claiming are not new to practitioners. However, in my experience, and as discussed below, rejections under the combination of 35 U.S.C. § 112(b) and (f) are increasing, and the USPTO is focusing on functional language as evidenced by recent training. For example, see Topic 6 of Executive Action 2, entitled “Claim Interpretation: Examining Functional Language,” which is scheduled to be completed by Spring 2015. 
In 2013, the PTAB published some informative decisions interpreting “processor for” and/or means-plus-function claim language under § 112. Most notably, in each of the decisions the PTAB entered a new ground of rejection sua sponte under both pre-AIA 35 U.S.C. § 112, second paragraph and sixth paragraph. Learning from the above decisions can provide some insight on how the PTAB and the CAFC analyze functional claim language, especially for inventions claiming the function of processors. Keeping the principles in mind while drafting applications and amending claims during prosecution will certainly provide for a stronger claim and therefore a higher quality patent.
Functional language does not, in and of itself, render a claim improper. However, as recently experienced in Williamson v. Citrix (en banc) and Robert Bosch, using functional language carries a significant risk of having the claim invalidated as indefinite following a determination that the claim invokes § 112(f) even when the patentee does not intend to have the claim treated under § 112(f).
Means-plus function claims are generally avoided because of their narrow scope and high-likelihood of invalidity. In fact, “means for” claiming has been on a steady decline for the past two decades.  The chart below (from patentlyo) shows the percentage of published non-provisional patent applications that include the term “means for” at least once in the claim set.
The scope of a means-plus function claim depends on the corresponding structure (e.g., algorithm) disclosed in the specification. With respect to literal infringement, if a claim as treated as a means-plus-function limitation, the accused device must employ means identical to or the equivalent of the structures, material, or acts described in the patent specification. At the USPTO, absent a determination that a claim limitation invokes 112 § (f), the broadest reasonable interpretation is not limited to the “corresponding structure…and equivalents thereof” provided in the specification and figures. There is no comparable mandate in the patent statute that relates the claim scope of non-§ 112(f) claims to particular matter found in the specification. Accordingly, one unnecessary result of claims that invoke § 112(f) is the scope of the claim may be unnecessarily narrowed to what is shown in the specification. Therefore, drafting claims that avoid the invocation of § 112(f) is the first line of defense for indefinites and unnecessarily narrowing the scope of the invention.
During prosecution and litigation, when a claim invokes §112(f), an analysis of whether the claim is indefinite under §112(b) is forced, which requires the claim to survive further scrutiny. When §112(f) was actually invoked, the Federal Circuit frequently found claims indefinite. In the 10 years prior to Nautilus v. Biosig Instruments, the Federal Circuit found means-plus-function claims indefinite 65% when indefiniteness was argued, as compared with non-means-plus-function claims, which were indefinite only 23% of the time.
Principles of Law
Use of the word “means” in a claim creates a rebuttable presumption that the applicant intended to invoke § 112(f). Failure to use the word “means” creates a rebuttable presumption that the applicant did not intend the claims to be governed by § 112(f).
Prior to the en banc opinion in Williamson v. Citrix, the presumption against invocation was characterized as ”strong.” Now, the standard “is whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure.” If the words of the claim do not meet the standard, then § 112(f) applies. The en banc opinion expressly overrules the characterization of the presumption as “strong.”
The above-recited standard is not a “new” one. Rather, it was the standard used prior to Lighting World, Inc. v. Birchwood Lighting, Inc. (Fed. Cir. 2004). Lighting World marked the first time a different standard was applied to the presumption flowing from the absence of the word “means” and held that the presumption flowing from the absence of the term “means” was a “strong one that is not readily overcome.” The en banc opinion reasoned that
the characterization is unwarranted, is uncertain in meaning and application, and has the inappropriate practical effect of placing a thumb on what should otherwise be a balanced analytical scale. It has shifted the balance struck by Congress in passing § 112, para. 6 and has resulted in a proliferation of functional claiming untethered to § 112, para. 6 and free of the strictures set forth in the statute.
The en banc opinion also overrules the raised bar of presumption set forth in Flo Healthcare Solutions, LLC v. Kappos (Fed. Cir. 2012). Flo Healthcare Solutions declared that “[w]hen the claim drafter has not signaled his intent to invoke [§ 112(f)] by using the term ‘means,’ [the CAFC] is unwilling to apply that provision without a showing that the limitation essentially is devoid of anything that can be construed as structure.” The en banc decision overruled the requirement of a “showing that the limitation essentially is devoid of anything that can be construed as structure.” The principle remains that the presumption that § 112(f) does not apply can be overcome if “the claim term fails to recite sufficiently definite structure or else recites function without reciting sufficient structure for performing that function.” 
Stated another way, the presumption may be overcome by using a term instead of “means” that is “a nonce word or a verbal construct that is not recognized as the name of structure.” Generic terms such as “mechanism,” “element,” “device,” and other nonce words that reflect nothing more than verbal constructs may be used in a claim in a manner that is tantamount to using the word “means” because they “typically do not connote sufficiently definite structure” and therefore may invoke § 112(f).
On the other hand, claim language that further defines a term that otherwise would be a nonce word can denote sufficient structure to avoid construction under § 112(f). A claim limitation that contains a term that is used in common parlance or by persons of skill in the art to designate structure, even if the term covers a broad class of structures and even if the term identifies the structures by their function can also denote sufficient structure. For example, “digital detector” was found to recite sufficient definite structure to avoid the invocation. “Digital detector” had a known meaning to those having ordinary skill in the art as a type of “detector” and dictionary definitions connoted structure, including a rectifier or demodulator.
The court also considers the specification to inform the analysis of whether the claim recites sufficiently definite structure to overcome a presumption that § 112(f) governs the claim. For example, in Inventio AG v. Otis Elevator Co., the claim terms “modernizing device” and “computing unit” when read in light of the specification connoted sufficient, definite structure to one of skill in the art to preclude application of § 112(f). Accordingly, the question becomes: would one having ordinary skill in the art recognize the relevant term as providing sufficiently definite structure for performing the claimed function?
The USPTO applies § 112(f) to a claim limitation if it meets the following 3-prong analysis:
- (A) the claim limitation uses the term “means” or “step” or a term used as a substitute for “means” that is a generic placeholder for performing the claimed function;
- (B) the term “means” or “step” or the generic placeholder is modified by functional language, typically, but not always linked by the transition word “for” or another linking word or phrase, such as “configured to” or “so that”; and
- (C) the term “means” or “step” or the generic placeholder is not modified by sufficient structure, material, or acts for performing the claimed function.
The Williamson v. Citrix en banc opinion effectively lowers the bar for overcoming the presumption that a limitation expressed in functional language without using the word “means” is not subject to § 112(f). Therefore, under this standard, functional claim terms may more readily be subject to § 112(f), which increases their risk of attack based on indefiniteness under § 112(b).
If § 112(f) applies to a claim limitation, then the claim is reviewed for indefiniteness in accordance with § 112(b) to determine whether the corresponding structures, materials, or acts that perform the claimed function are disclosed in the specification. If the corresponding structure is not adequately disclosed, then the claim will be indefinite under § 112(b). The trade-off for allowing means-plus function claiming is that the specification must contain sufficient descriptive text by which a person of skill in the field of the invention would know and understand what structure corresponds to the limitation invoking § 112(f).
In computer-implemented inventions, the corresponding structure must be an algorithm, disclosed as one or more flow charts supported by a written description of each step. In particular, as stated in Aristocrat Techs. Australia Pty Ltd. v. Int’l Game Tech, the corresponding structure must include the algorithm needed to transform the general purpose computer or processor disclosed in the specification into the special purpose computer programmed to perform the disclosed algorithm. 
The “specification can express the algorithm in any understandable terms including as a mathematical formula, in prose, or as a flow chart, or in any other manner that provides sufficient structure.” An algorithm is defined, for example, as “a finite sequence of steps for solving a logical or mathematical problem or performing a task.”
Structure disclosed in the specification qualifies as “corresponding structure” if the intrinsic evidence clearly links or associates that structure to the function recited in the claim. Therefore, “if a person of ordinary skill in the art would be unable to recognize the structure in the specification and associate it with the corresponding function in the claim, a means-plus-function clause is indefinite.”
With respect to adequate disclosure in the specification, simply disclosing a computer as the structure designated to perform a particular function does not limit the scope of the claim to “the corresponding structure, material, or acts,” that perform the function, as required by section § 112.
In Eon Corp., finding the claims indefinite, the CAFC distinguished the case from that of In re Katz, which held that a standard microprocessor can serve as sufficient structure for “functions [that] can be achieved by any general purpose computer without special programming.” In Katz, claim terms involving basic “processing,” “receiving,” and “storing” functions were not necessarily indefinite because a general purpose computer need not “be specially programmed to perform the recited function.” The court called this exception a narrow one. The claims in Eon Corp. were indefinite since a general purpose microprocessor could not perform the functions claimed, such as “causing selected themes to automatically display a second menu.”
In Noah Sys. Inc. v. Intuit Inc., the CAFC reiterated that the test for definiteness asks whether one skilled in the art would understand the bounds of the claim when read in light of the specification.” However, the testimony of one of ordinary skill in the art cannot supplant the total absence of structure from the specification.” 
In addition, relying on the proposition that the algorithm, which is lacking in the specification, is known to one of ordinary skill in the art does not save the claim from indefiniteness.” Further, a bare statement that known techniques or methods can be used does not meet the standard for adequately disclosing structure. The CAFC in Triton Tech of Tex., LLC v. Nintendo of Am., Inc. upheld indefiniteness of a claim stating that “the district court correctly recognized that ‘[a]lthough a person of skill in the art might be able to choose an appropriate numerical integration algorithm and program it onto a microprocessor, the [p]atent discloses no algorithm at all.’” So, extrinsic evidence in the form of dictionaries may be used as evidence to determine whether a term connotes structure to avoid the invocation a claim under § 112(f), but testimony alone will not cure indefiniteness of the claim under § 112(b) if the algorithm is not disclosed.
Practitioners must be aware that § 112(f) may be unintentionally invoked when functional claim language is used to define the metes and bounds of an invention. When a claim invokes § 112(f), the disclosure must adequately describe the structure, material or acts to perform the function, or else the claim will be invalid as indefinite under § 112(b). The risk of having functional language invoke § 112(f) is that it increases the risk that the claim may be found indefinite under § 112(b). Therefore, considering whether a claim term may invoke § 112(f) is especially important for computer-implemented inventions since functional claim language is often used. Careful attention should also be given to functional language in view of the en banc decision, which abandoned the characterization that the presumption against the invocation of §112(f) is “strong” when “means” is not recited.
In addition, the USPTO have taken numerous steps to improve claim clarity and scrutinize functional limitations, including training examiners on handling functional claims. The office has implemented a multi-phased training program for all examiners that focuses on evaluating functional claiming and improving the clarity of the examination record. Accordingly, the Examining Corp and the PTAB are focusing on this issue. Therefore, practitioners should equally focus on this issue.
One strategy is to draft claims that avoid the invocation in the first place and to have an adequate disclosure in case the claim is found to invoke § 112(f). In general, the invocation is avoided by 1) not using means-plus-function format (e.g., “’means for…”); and 2) claiming enough structure, material, or acts to perform the function. As stated in Williamson v. Citrix (en banc), the standard is whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure. Therefore, practitioners should avoid using terms in the claim that do not have a meaning to those having ordinary skill in the art to connote structure. The written description should also be clear in describing the components of the structure that perform the claimed function and how they are linked or associated with the function.
Part 2 of this article focuses on how the CAFC has applied some of these principles by analyzing recent decisions.
 Williamson v. Citrix, No. 13-1130, slip op. at 15-16 (Fed. Cir. 2015)
 35 U.S.C. § 112 was amended and subsections were renamed by the America Invents Act, Pub. L. No. 112-29 (“AIA”), which took effect on September 16, 2012. For simplicity,
pre-AIA 35 U.S.C. § 112, second paragraph will be referred to as § 112(b), and pre-AIA 35 U.S.C. § 112, sixth paragraph will be referred to as § 112(f)
 Robert Bosch, LLC v. Snap-On Inc., 769 F.3d 1094 (Fed. Cir. 2014)
 M.P.E.P. 2173.05(g)
 The USPTO will continue training based on Executive Action 2, which is one of five executive actions “to help bring about greater transparency to the patent system and level the playing field for inventors.” Executive Action 2 is titled “Clarity in Patent Claims (formerly “Tightening Functional Claiming”). See http://www.uspto.gov/patent/initiatives/uspto-led-executive-actions-high-tech-patent-issues#heading-3; Topic 6 entitled “Claim Interpretation: Examining Functional Claim Language” is slated to begin Spring 2015.
 M.P.E.P. 2173.05(g)
 In re Morris, 127 F.3d 1048, 1055 (Fed. Cir. 1997)
 Id. at 1055; see also M.P.E.P. 2181
 Jason Rantanen, Teva, Nautilus, and Change Without Change, (March 26, 2015). Stanford Technology Law Review, 2015; U Iowa Legal Studies Research Paper No. 15-07. Available at SSRN:http://ssrn.com/abstract=2585844
 Id. at 17.
 Personalized Media Comm’ns, LLC v. Int’l Trade Comm’n, 161 F.3d 696, 703 (Fed. Cir. 1998); Flo Healthcare Solutions, LLC v. Kappos, 697 F.3d 1367, 1373 (Fed. Cir. 2012).
 Williamson v. Citrix, No. 13-1130, slip op. at 16 (Fed. Cir. 2015); Also note that the en banc opinion cites Greenberg v. Ethicon Endo-Surgery, Inc., 91 F.3d 1580, 1583 (Fed Cir. 1996) for this standard.
 Id. at 15-16
 Id. at 15
 Id. at 14
 Id. at 15
 Id. at 16
 Id.; Lighting World, Inc. v. Birchwood Lighting, Inc., 382 F.3d 1354, 1358 (Fed. Cir. 2004) (quoting CCS Fitness, Inc. v. Brunswick Corp., 288 F.3d 1359, 1369 (Fed. Cir. 2002); Watts v. XL Sys., 232 F.3d 877, 880 (Fed. Cir. 2000)
 Lighting World at 1360.
 Mass. Inst. of Tech. & Elecs. for Imaging, Inc. v. Abacus Software, 462 F.3d 1344, 1354 (Fed. Cir. 2006); see generally M.P.E.P. § 2181.
 MIT v. Abacus Software, 462 F.3d 1344, 1354 (Fed. Cir. 2006)
 Lighting World at 1359 (quoting Ethicon Endo-Surgery, Inc., 91 F.3d 1580, 1583 (Fed. Cir. 1996) (“Many devices take their names from the functions they perform.”))
 Personalized Media Comm’ns at 704.
 Id. at 705
 M.P.E.P. 2181
 Personalized Media at 703.
 Id. at 10 (quoting Finisar Corp. v. DirecTV Grp., Inc., 523 F.3d 1323, 1340 (Fed. Cir. 2008)).
 Aristocrat Techs. Australia Pty Ltd. v. Int’l Game Tech., 521 F.3d 1328, 1333 (Fed. Cir. 2008).
 Functional Media v. Google, 708 F.3d 1310, 1317-18.; Ex parte lakallak quoting Finisar Corp. v. DirecTV Group, Inc., 523 F.3d 1323, 1340 (Fed. Cir. 2008)
 Finisar Corp. v. DirecTV Group, Inc., 523 F.3d 1323, 1340 quoting MICROSOFT COMPUTER DICTIONARY 23 (5th ed. 2002)
 Williamson v. Citrix, en banc (2015); Noah Sys. Inc. v. Intuit Inc., 675 F.3d 1302, 1312 (Fed. Cir. 2012)
 Id. at 1333
 In re Katz Interactive Call Processing Patent Litig., 639 F.3d 1303 (Fed. Cir. 2011)
 Id. at 1316
 Noah Sys. Inc. v. Intuit Inc., 675 F.3d 1302 (Fed. Cir. 2012)
 Id. at 1312, citing Default Proof Credit Card Sys., Inc. v. Home Depot U.S.A., Inc., 412 F.3d 1291, 1302 (Fed. Cir. 2005)
 Triton Tech of Tex., LLC v. Nintendo of Am., Inc., 753 F.3d 1375, 1378 (Fed. Cir. 2014) (quoting Biomedino, LLC v. Waters Techs. Corp.., 490 F.3d 946, 953 (Fed. Cir. 2007); see also ePlus, Inc. v. Lawson Software, Inc., 700 F.3d 509, 519 (Fed. Cir. 2012))
 Id. at 1379
 Williamson v. Citrix Online, LLC, No. 13-1130 (Fed. Cir. Nov. 5, 2014), discussed infra