The Yale Law Journal


And How: Mayo v. Prometheus and the Method of Invention

01 Apr 2013
Jacob S. Sherkow


In Mayo Collaborative Services v. Prometheus Laboratories, Inc.,1 the Supreme Court invalidated the asserted patents’ process claims as unpatentable subject matter under § 101 of the patent statute.2 The Court gave three principal justifications for its rejection. First, the process claims were directed to “laws of nature, natural phenomena, and abstract ideas.”3 Second, in any event, the patent did not contain enough of an “inventive concept” to ensure that it “amounts to significantly more than a patent upon the natural law itself.”4 And third, the invention involved “well-understood, routine, conventional activity, previously engaged in by researchers in the field.”5

Much has been written—and will continue to be written—about those first two justifications. But commentators thus far have paid less attention to the third. Interestingly, the third justification is quite different from the first two. Rather than focusing on what the invention is, it focuses on how the invention is accomplished. That is, the Court’s first two justifications concern the characterization of the invention itself: the thing or process purported to be invented, the language of the claims, and the significance of the invention to the field. The third justification, however, concerns the method by which the invention is implemented, whether a “conventional activity” or a unique method.

Given the novelty of that justification6 (and how recently Mayo was decided), the consequences of the additional inquiry remain unclear. Nonetheless, the Mayo Court’s new focus on how an invention is conceived—a condition on which patent eligibility depends—appears to pose several doctrinal and practical difficulties. First, it fails to distinguish true “inventions” from unpatentable abstractions in contravention of § 101’s historical purpose. Second, it confusingly overlaps with another requirement in the patent statute: nonobviousness. Third, it violates the principle that patent eligibility should not be tied to “the manner in which the invention is made.” And last, it requires the patent office to engage in “on the ground” factfinding, even though there are scant administrative procedures for that task.

I. Failing To Distinguish Abstractions

A requirement to consider how an invention operates does not fulfill the historical purpose of § 101: to distinguish patent-eligible “inventions” from unpatentable abstractions.7 The Supreme Court’s prior interpretations of § 101 embody this concern.8 Although § 101’s text does not define the concept of “invention,” it permits a patent application for “any new and useful process, machine, manufacture, or composition of matter.”9 The statute’s broad language has long been thought to encompass “anything under the sun made by man”10 and to serve as little more than a threshold inquiry.11 Nonetheless, this threshold inquiry made ineligible patent applications involving abstract ideas, mathematical equations, or mental processes.12 Yet it also left other applications to the remaining rigors of the patent statute.13 Even then, § 101 was not thought to prohibit patents monopolizing discrete applications of such abstractions, such as manufacturing equipment that relied on certain mathematical formulae.14

The Court’s novel patent-eligibility test—rendering ineligible inventions involving “well-understood, routine, conventional activity, previously engaged in by researchers in the field”15—does little to accomplish the goal of distinguishing “inventions” from “abstractions.” Because inventions, both physical and abstract, operate in a variety of ways, an examination of how they operate fails to separate the concrete from the conceptual. Both physical and abstract inventions, for example, can call upon “well-understood, routine, conventional activity.” Many inventions in the life sciences, for example, use well-understood, routine, and conventional mechanisms, even though they concretely apply to real world phenomena.16 At the same time, new and useful, but abstract, mathematical proofs may rely on poorly understood, infrequently used, unorthodox mechanisms to obtain their results.17 The Court’s inquiry into how an invention or an idea solves a particular problem does no work to distinguish between inventions and ideas themselves.

II. Overlapping with Obviousness

The Mayo Court’s concern with how an invention is accomplished, relative to the state of the art in its field, overlaps with the patent statute’s proscription against “obviousness,” thus rendering much of it superfluous. Section 103 of the patent statute denies a patent to an invention “if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art.”18 That standard necessarily requires some inquiry into how the invention solved a problem in its field, specifically, whether the invention uses old or new methods.19

Section 103’s standard significantly overlaps with the Mayo Court’s view of patent eligibility as turning on “well-understood, routine, conventional activity, previously engaged in by researchers in the field.”20 The two inquiries share multiple, similar concerns that are difficult to distinguish: (1) routine vs. ordinary activity; (2) a researcher in the field vs. a person having ordinary skill in the art; and (3) previous engagement vs. activity before the effective filing date of the invention. What is the significant difference, for example, between a “researcher in the field” and a “person having ordinary skill in the art”? The Mayo Court’s conception of patent eligibility almost swallows obviousness as a condition for patentability. Indeed, it is difficult to conceive of the invention that does not involve “well-understood, routine, conventional activity, previously engaged in by researchers in the field,”21 but is “obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art.”22 The “how” of the Mayo Court’s patent eligibility inquiry appears to diminish the “how” of the obviousness requirement.23

III. Discriminating Against the “Manner of Invention”

Similarly, the Court’s concern with how an invention is created may violate § 103’s bar against “negat[ing],” i.e., denying, patentability according to “the manner in which the invention was made.”24 This protection seeks to treat equally inventions made by “long toil and experimentation” and those created in a “flash of genius.”25 Yet denying patent eligibility to inventions that operate through “well-understood, routine, conventional activity” may discriminate against inventions made by “long toil and experimentation.” The reason is that inventions employing “well-understood, routine, conventional activity” are often created through “long toil and experimentation.” Inventions in chemistry or molecular biology, for example, frequently operate using “well-understood, routine, conventional” mechanisms, such as drugs developed by traditional chemical-screening methods.26 In the fields of chemistry and biology, advances in those mechanisms are typically introduced through “trial and error” rather than sudden “flashes of genius.”27 In contrast, inventions that work in an unconventional manner are often the result of creative syntheses across multiple technologies that stem from “flashes of genius.”28

The patent in Mayo illuminates this point. That patent claimed a method of optimizing a patient’s drug dosage by measuring a particular metabolite in the patient’s blood—a “well understood, routine, and conventional” method for altering drug dosage.29 It is unsurprising, therefore, that the key to the invention—the ability to determine the particular level of the metabolite—was ascertained through rigorous clinical studies,30 exemplars of “long toil and experimentation” rather than “flashes of genius.” In that sense, denying patent eligibility according to howaninvention works essentially negates patentability according to its method of invention.31

IV. Requiring Administrative Factfinding

The addition of “how” to the patent eligibility inquiry poses administrative difficulties as well. Asking whether an activity involves “well-understood, routine, conventional activity, previously engaged in by researchers in the field”32 would require the U.S. Patent and Trademark Office (PTO) to actually determine whether researchers in the field considered an activity routine or conventional, and whether those researchers had truly engaged in that activity. The PTO is poorly equipped to handle that inquiry. Much of the PTO’s current work involves assessing prior art: reading technical documents to ascertain whether a patent application is “new” or “nonobvious” in the field.33 Although the Court’s “well-understood, routine, conventional activity” test greatly overlaps with “nonobviousness,”34 prior art seems ill-equipped to prove “routine” or “convention.” Rather, questions concerning an activity’s routineness or conventionality, and questions whether researchers have performed that activity, appear much more rooted in an on-the-ground factual assessment. “Routine” and “convention” are issues of practice, not necessarily publication, and there may be a significant delay between when researchers begin to engage in such activities and when they publicly declare they are doing so.35 In other areas, such as the Daubert standard for the admissibility of scientific evidence,36 surveying the landscape of complex technical practice is often better left to witnesses rather than documentary testimony.37 Currently, however, the PTO has few administrative procedures to hear such testimony.38 Nor does there seem to be any movement to expand them.39 Despite the Court’s interest in tying patent eligibility to practical activity, it is unclear how the PTO will obtain the tools it needs to make such assessments. The PTO’s expertise, rather, lies in determining what inventions are, not how those inventions were made.


The future will tell whether this philosophical shift in patent eligibility, from what to how, will have the legal effects discussed in this Essay. If it does, its practical effects will likely be felt across all levels of the patent complex: research, invention, prosecution, enforcement, litigation, and licensing. Research institutions concerned with obtaining intellectual property for their investments will likely steer funds away from “conventional” research. The PTO will need to equip itself with the proper administrative tools to assess on-the-ground research behavior. Inventors will likely paint their claims with more detail to give the impression that their methods are not routine in the field. And litigators will be even more encouraged to canvass scientific experts to testify that a scientific method is, or is not, “well-understood.”

All of that work will be devoted to analyzing whether an invention is even eligible to be patented, let alone valid or invalid under the remaining portions of the statute. As previous assessments of patent eligibility were rooted in more facial inquiries, such as whether an invention was “abstract,” the Court’s recent focus on the method of invention is a difference not just in degree, but in kind. Patent practitioners will need to prepare for these changes—and how.

Jacob S. Sherkow is a fellow at the Center for Law and the Biosciences at Stanford Law School. He gives thanks to Hank Greely, Mark A. Lemley, Matt Lamkin, and Sarah R. Wasserman Rajec for their comments.

Preferred citation: Jacob S. Sherkow, And How: Mayo v. Prometheus and the Method of Invention, 122 Yale L.J. Online 351 (2013),