Functional Claims in US Patents: Past, Present, and Future

Published Date
Sep 22, 2023
Related people
IP Litigation Associate, Colby Davis, looks at so-called “functional” claims under US patent law.

Before the Civil War, the famed inventor, Samuel Morse, sought patent protection for a revolutionary discovery, electronic messaging:  “I do not propose to limit myself to the specific machinery or parts of machinery described in the foregoing specification and claims; the essence of my invention being the use of . . . electro-magnetism, however developed, for making or printing intelligible characters, signs or letters at any distances . . ..”  This is so-called “functional” patent claiming, i.e., patenting an effect, result, or general steps for achieving a result (electronic messaging), rather than a specific structure, machine, or process (telegraph).  In a precedent widely cited to this day, the Supreme Court rejected Mr. Morse’s claim:  “[O]ne may lawfully accomplish the same end without infringing the patent, if he uses means substantially different from those described.”  O’Reilly v. Morse, 56 U.S. 62, 119 (1854).  Thus, if text messaging, email, and WhatsApp “use[] means substantially different from” telegraphing, Mr. Morse’s patent would not bar introduction of those technologies by a competitor. 

The Court’s emphasis on “means substantially different” foreshadowed enactment of Section 112(f) of the US Patent Act almost a century later by the Congress of 1952, codifying what we now call “means-plus-function” claim elements:

“An element . . . may be expressed as a means or step for performing a specified function without the recital of structure . . . and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.”

35 U.S.C. § 112(f).  Both then and now, inventors such as Morse may not patent all ways of achieving an end-result, such as electronic messaging. 

However, as US courts struggle to define the boundaries of what constitutes a patentable (35 U.S.C. § 101) and sufficiently enabled (35 U.S.C. § 112(a)) invention, the analysis returns time and again to Morse and the limits of “functional” claiming.  See, e.g., Amgen Inc. v. Sanofi, 143 S. Ct. 1243, 1256 (2023) (invalidating patents for lack of enablement where “Amgen s[ought] to monopolize an entire class of things defined by their function” ); IBM v. Zillow Grp., Inc., 50 F.4th 1371, 1378 (Fed. Cir. 2022) (“A claim that merely describes an effect or result dissociated from any method by which it is accomplished is usually not directed to patent-eligible subject matter.”) (cleaned up).  

If Congress or the courts are to “fix” Section 101, as many commentators request, or enablement in the wake of Amgen, the solution will have something to do with functional claiming.  But Congress and the courts have been attempting to “fix” the same problem for as long as the nation has existed.   Whittemore v. Cutter, 29 F. Cas. 1123, 1124 (C.C.D. Mass. 1813) (“A patent can, in no case, be for an effect only, but for an effect produced in a given manner, or by a peculiar operation.”).  That history is widely forgotten in debates over the future of the Patent Act and 21st Century innovation.

A Brief History of “Functional” Claiming

Morse was by no means the first case of its kind.  See, e.g., Wyeth v. Stone, 30. F. Cas. 723, 730, 1840 U.S. App. LEXIS 534, *23 (C.C.D. Mass 1840) (invalidating patent for the manufacture of any ice-cutting machine that does not rely on mechanical human power); Leroy v. Tathum, 55 U.S. 156, 175 (1852) (invalidating patent on any machine for forming cast lead pipe by reuniting recently set pieces under heat and pressure in a closed vessel).  And for a century after Morse, as before, courts invalidated numerous patents based on functional claim language, sometimes without even identifying a specific statutory basis.  See, e.g., Morton v. New York Eye Infirmary, 5 Blatchf. 116 (S.D.N.Y. 1862) (invalidating patent on any means for anesthetizing patients for surgery by the inhalation of ether); Marachand v. Emken, 132 U.S. 195, 200 (1889) (denying patent for any machine applying a vortex in the production of hydrogen peroxide); In re Haas, 81 F.2d 408 (C.C.P.A. 1936) (invalidating patent on preventing bread mold by use of any machine that surrounds the knives and not merely the bread in a stream of sterile air). 

By World War II, the jurisprudence on functional claiming was more nuanced, accepting ancillary functional claim language, while banning altogether “functional claiming at the exact point of novelty.”  General Electric Co. v. Wabash Appliance Corp., 58 S.Ct. 899, 903 (1938); see also, e.g., Halliburton Oil Well Cementing Co. v. Walker, 329 U.S. 1, 12 (1946) (“[U]nless frightened from the course of experimentation by broad functional claims like these, inventive genius may evolve many more devices to accomplish the same purpose.”).  Thus, with varying statutory bases in the Patent Act, courts honed in on the “point of novelty” or “inventive step,” invalidating patents with functional language in those critical claim limitations.  See, e.g., In re Fullam, 34 C.C.P.A. 1018, 1021 (C.C.P.A. 1947) (“[T]he critical material is defined solely in terms of what it will do, and that claim is, therefore, functional and unpatentable.”).

“Congress enacted § 112, P6 in response to Halliburton Oil[.]” Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 27 (1997) (collecting cases).  “In place of the Halliburton rule, Congress adopted a compromise solution, one that had support in the pre-Halliburton case law:  Congress permitted the use of purely functional language in claims, but it limited the breadth of such claim language by restricting its scope to the structure disclosed in the specification and equivalents thereof.”  Greenberg v. Ethicon Endo-Surgery, Inc., 91 F.3d 1580, 1582 (Fed. Cir. 1996).  While some Federal Circuit judges contend “this rationale applies to functional claiming generally, not just to claims that recite ‘means’” (Williamson v. Citrix Online, LLC, 792 F.3d 1339, 1358 (Fed. Cir. 2015) (Reyna, J., concurring)), courts initially “established a heightened bar to overcoming the presumption that a limitation expressed in functional language without using the word ‘means’ is not subject to § 112, para. 6” (id. at 1358).  That heightened bar to application of Section 112(6) has begun eroding in recent years.  See, e.g., MTD Prods. Inc. v. Iancu, 933 F.3d 1336, 1341 (Fed. Cir. 2019) (“Generic terms like ‘module,’ ‘mechanism,’ ‘element,’ and ‘device’ are commonly used as verbal constructs that operate, like ‘means[.]’”).

Courts Are Looking at Functional Claiming Beyond Section 112(f)

While restrictive application of Section 112(f) is widely viewed as innovator-friendly, the result has been increased scrutiny of functional or quasi-functional claims in other areas of US patent law, including in the analysis of patent eligibility, enablement, and written description.  Indeed, searching for the ever-elusive definition of an “abstract idea” under Section 101, at least Judge Reyna believes that “abstract” in this context is roughly synonymous with “functional”:  “Based on the Supreme Court’s use of the abstract idea exception, it is apparent that a desired goal (i.e., a ‘result or effect’), absent structural or procedural means for achieving that goal, is an abstract idea.”  Amdocs (Isr.) Ltd. v. Openet Telecom, Inc., 841 F.3d 1288, 1309 (Fed. Cir. 2016).  The same language, closely mirroring that of Halliburton and Wabash Appliance, is increasingly emphasized in opinions invalidating patents under Section 101.  See, e.g., RecogniCorp, LLC v. Nintendo Co., 855 F.3d 1322, 1326 (Fed. Cir. 2017) (“The inquiry often is whether the claims are directed to ‘a specific means or method’ for improving technology or whether they are simply directed to an abstract end-result.”); Interval Licensing LLC v. AOL, Inc., 896 F.3d 1335, 1345 (Fed. Cir. 2018) (“Instead of claiming a solution for producing that result, the claim in effect encompasses all solutions.”).  

In May, the Supreme Court never mentioned Section 112(f) en route to invalidating blockbuster pharmaceutical patents, on the grounds that “Amgen s[ought] to monopolize an entire class of things defined by their function.”  Amgen Inc. v. Sanofi, 143 S. Ct. 1243, 1256 (2023); see also Amgen Inc. v. Sanofi, 987 F.3d 1080, 1087 (Fed. Cir. 2021) (“While functional claim limitations are not necessarily precluded in claims that meet the enablement requirement, such limitations pose high hurdles in fulfilling the enablement requirement for claims with broad functional language.”).  Early cases applying Amgen indicate that the enablement inquiry will now closely scrutinize functional or quasi-functional claim elements, potentially leading to increased invalidity rulings under Section 112(a), as occurred previously with Section 101.  See, e.g., Orexo AB v. Sun Pharm. Indus., No. 3:20-cv-12588-GC-DEA, 2023 U.S. Dist. LEXIS 120114, at *74 (D.N.J. June 30, 2023) (“Amgen reaffirmed that when a party ‘monopolize[s] an entire class of things defined by their function,’ the party must enable a POSA to make and use the entire class.”) (quoting Amgen, 143 S. Ct. at 1256). 

An Old Solution for a Supposedly New Problem

As the above history suggests, analysis under Sections 101 and 112 increasingly overlaps, seeking to place limits on functional claim language.  And many commentators have sought Congressional intervention to “fix” the jurisprudence, such as Senator Tillis’ Patent Eligibility Restoration Act of 2022, S.4734.  But they say history repeats itself, and the Congress of 1952 apparently believed it had “fixed” the very same problem by shifting disputes from validity of functional patent claims to scope and infringement.  See 35 U.S.C. § 112(f) (“cover the corresponding structure . . . in the specification and equivalents thereof”).

For software patents, and especially machine learning or AI patents, some functional claiming is likely inevitable, and perhaps even innovators would prefer to litigate the doctrine of equivalents under Section 112(f), rather than testing the full potential breadth of quasi-functional (but not formally means-plus-function) claim language under Sections 101 and 112(a).  That is, as the risk of invalidation under Sections 101 and 112(a) increases for inventions such as machine learning or AI, innovators may counterintuitively press for claim construction under Section 112(f), risking non-infringement instead.  There is risk, to be sure, in either approach, but at least there is a reasonably agreed definition for “equivalents,” which cannot be said for “abstract ideas.”  Predictability is a value in itself.

In short, before asking Congress to “fix” the Patent Act, we might look to history and ask if they “fixed” it already, at least for functional claim language.  Perhaps a more modest goal for a congressional or jurisprudential “fix” is in order—merely effectuating the original intent of the Congress of 1952 in enacting the language of Section 112(f).

Content Disclaimer
This content was originally published by Allen & Overy before the A&O Shearman merger

Related capabilities