According to the U.S. Supreme Court, the judicial exceptions to this clause are about 50 years younger: “‘We have long held that [35 U.S.C. § 101] contains an important implicit exception: Laws of nature, natural phenomena, and abstract ideas are not patentable.’ We have interpreted § 101 and its predecessors in light of this exception for more than 150 years.”3 And, “these exceptions have defined the reach of the statute as a matter of statutory stare decisis going back 150 years.”4
The Origin of the Judicial Exceptions
Since the start of the twentieth century, at least 10 Supreme Court cases have directly addressed the issue of patent-eligible subject matter.5 Of these, only one case states, briefly, the origin of the judicial exceptions: “In reviewing earlier cases applying the rule that a scientific principle cannot be patented, the Court placed particular emphasis on the English case of Neilson v. Harford, Web. Pat. Cases 295, 371 (1844).”6
The Supreme Court imported the judicial exceptions entirely from English common law. Historically speaking, this is not unusual. In the early years of the United States, the Supreme Court imported English and British law to fill gaps in U.S. case law. Even today, the Supreme Court looks occasionally to old English law to trace the development of legal principles to their origins before U.S. independence.7 The high courts in Commonwealth countries have done the same.
The purpose of this article is to summarize, as a general matter, what the English common law of patent-eligible subject matter was at the time of the early United States. At first glance, one may ask why such a summary is relevant to modern U.S. patent law. In In re Bilski, Judge Dyk in his concurrence answers this question by reviewing the legislative history of the U.S. Patent Act of 1793, which showed clearly that Congress intended to adopt and codify most of the British patent regime.8 Therefore, it would not be a stretch to imagine that Congress intended for the Court to turn to British common law for guidance when interpreting the Patent Act of 1793. As far as I know, Judge Dyk’s concurrence in In re Bilski is the only appellate court opinion that has framed § 101 jurisprudence through the historical lens of old English and British patent law.9
“Manufactures” in the Statute of Monopolies
Due to perceived abuses by the Crown, the Parliament of England10 passed in 1624 the Statute of Monopolies, which banned all state-sanctioned monopolies except for limited-time monopolies to inventors of “new manufactures.”
[A]ny declaration, before-mentioned, shall not extend to any letters patent and grants of privilege for the term of fourteen years, or under, hereafter to be made, of the sole working or making of any manner of new manufactures within this realm, to the true and first inventor and inventors of such manufactures . . . .11
Bottom line up front, today’s jurisprudence on § 101 begins with the old English courts’ statutory interpretation of the word “manufactures” in the Statute of Monopolies. In fact, this is the starting point for all Anglo-American and Commonwealth jurisprudence on the issue of patent-eligible subject matter, as indicated by citations to English cases in U.S., Canadian, and Australian decisions.12 In these early English cases, the issues were (1) whether a “principle” constituted a manufacture under the Statute of Monopolies, and (2) whether the patent at hand claimed a principle.
The litigation that brought about this statutory interpretation of “manufactures” arose from disputes regarding three patents during the English Industrial Revolution: Watt’s patent for the improved steam engine, Minter’s patent for the reclining chair, and Neilson’s patent for the hot blast furnace. This period of litigation spanned over a half-century (1795–1843) and involved cases from the trial courts (Court of Common Pleas) up to the highest court of appeal (House of Lords). Like today, such extensive litigation was expensive, and enormous profits and losses were at stake.13
Making Sense of Old English Case Law
There are two reasons why it would be difficult for today’s patent lawyer to read and understand the old English case law. First, the patent laws of that time were, by today’s standards, very convoluted and undeveloped. The patentability requirements (today’s §§ 101, 102, 103, and 112) were not necessarily analyzed separately as they are today. In the English cases, most of the discussion on patent-eligible subject matter is found in dicta tied to other issues that are not relevant in modern U.S. patent law. Also, modern patents have separate sections in the specification for the claims and the written description, whereas the old English patents had a unified specification that did not explicitly point out the claims.14
Second, these early patent cases contained multiple, simultaneous issues of first impression for the English courts. Even more, judges would admit that it was difficult for the court to wrap its head around the issues and come to a reasoned opinion.15 This can make the written opinions a difficult read. Nonetheless, this article is an attempt to provide a synopsis of the relevant portions of these cases in an easy-to-understand, yet accurate, summary.
The Watt Cases: The Origin of “Principles”
Watt’s Patent on Steam Engine Condensers
The Crown granted a patent to James Watt on January 5, 1769, for a “method of lessening the consumption of steam, and consequently fuel in [steam] engines.”16 Today, we would understand this to be a process patent.
Watt’s invention was a method of improving the efficiency of the previously existing steam engine design. In atmospheric-pressure steam engines, a piston is driven back and forth through the open end of a cylinder—the other end being closed—by the pressure difference between the natural atmosphere outside the cylinder and the artificial pressure inside the cylinder. The artificial pressure would be increased by flowing steam into the cylinder from an external boiler. Conversely, the artificial pressure would be decreased by cooling the steam inside the cylinder. The technological issue at hand was how to cool this steam.
In previous designs, the artificial pressure would be decreased by directly cooling the cylinder with water, thereby cooling the steam inside of the cylinder. Watt’s invention was to add a condenser external to the cylinder that would receive the hot steam from the cylinder, cool it, and flow it back into the cylinder.17 Watt’s condenser improved the steam engine by allowing the cylinder to remain hot, thus shortening the time and energy required for each stroke of the piston.
Watt pleaded infringement claims against both Edward Bull (a former employee of Watt) and Jabez Carter Hornblower (a steam engine designer and manufacturer). Both defendants argued that Watt’s patent was invalid because it claimed ineligible subject matter. One of the defendants’ invalidity arguments was that the first sentence of Watt’s specification used the word “principles.”18 Thus, the invalidity issue was whether Watt’s “principles” constituted patentable manufactures under the Statute of Monopolies.
Boulton v. Bull
Boulton v. Bull was the first case in English jurisprudence on the patent ineligibility of principles.19 The trial court had a difficult time grappling with the issue because there was no precedent on the matter in 1795.20 After a lengthy analysis by each judge, most of which addressed issues other than the issue of claiming a principle, the Boulton court was split on the final ruling.21
Hornblower v. Boulton
The Boulton split was resolved by an appellate court in Hornblower v. Boulton,22 which was an infringement case on the same patent from the same trial court but with a different defendant. Specifically, the defendant argued that Watt’s patent was invalid because it was directed to “mere principles only, for which no such letters patent could by law be granted.”23 The appellate court ruled unanimously that Watt’s patent was valid because it did not claim a principle, despite the use of the word “principle” in the specification.24 The court never ruled unanimously on whether a principle, in general, is a patent-eligible manufacture under the Statute of Monopolies, although the judges seemed to indicate that it was not.25 Despite this ambiguity, later English and U.S. courts view Hornblower as standing for the proposition that principles are not patent-eligible subject matter.
Takeaways from the Watt Cases
In patent jurisprudence, the Watt cases are remembered and cited for the proposition that principles are not patent-eligible subject matter under the Statute of Monopolies. However, there are two interesting historical notes from the Watt cases that are not normally mentioned. First, the use of the word “principles” in all Anglo-American patent eligibility jurisprudence arises simply from a patent drafter’s choice of words in Watt’s patent from 1769. Second, process patents have been the major source of patent eligibility issues since the beginning. Here, Watt’s patent was what today would be considered a process patent. Likewise, many § 101 cases from the U.S. Supreme Court dealt with processes, such as Gottschalk, Flook, Diehr, Bilski, Mayo, and Alice.
Minter’s Case: The New Application of a Previously Known Principle
Minter’s Patent on the Reclining Chair
The Crown granted a patent to George Minter on November 9, 1830, for “an improvement in the constructing, making and manufacturing of chairs.”26 The patent claimed “the application of a self-adjusting leverage to the back and seat of a chair, whereby the weight on the seat acts as a counterbalance to the pressure against the back of such chair.”27 Today, we would understand this to be a product patent.
Motion to Dismiss in Minter v. Wells
In Minter v. Wells, the defendant moved to dismiss the infringement action, arguing that Minter’s patent for a reclining chair was invalid because it claimed “a first principle in mechanics, viz. the lever, and therefore nobody else may use it.”28 Specifically, the defendant argued that the patent was for “nothing more than the motion of a lever backwards and forwards, producing such an effect.”29
The defendant stated the law on patent eligibility as being, “[e]ither the plaintiff claims a principle, or he does not; to the former he is not entitled.”30 This appears to be the first characterization of Hornblower as standing for the proposition that principles are not patent-eligible subject matter, and the court did not disagree with this characterization.
The court ruled that the patent did not claim a principle but instead claimed “every machine consisting of a self-adjusting leverage producing that particular effect in a chair.”31 The court adopted this construction because the specification stated, “I do not confine myself to the particular shape of this lever.”32 After construing the patent as claiming a “machine,” albeit a very generalized machine, the defendant withdrew his motion to dismiss.33
The takeaway from the Minter case is that the court saw Minter’s patent was a new application of a previously known principle, which constituted a patent-eligible manufacture under the Statute of Monopolies. The known principle was the physics of leverage, and the new application was “the application of a self-adjusting leverage to the back and seat of a chair, whereby the weight on the seat acts as a counterbalance to the pressure against the back of such chair.” However, would the court rule the same if the patent was for an application of a previously unknown principle? Such was the issue in the Neilson cases.
The Neilson Cases: The Application of a Previously Unknown Principle
Neilson’s Patent on Hot Blast Furnaces
The Crown granted a patent to J.B. Neilson on September 11, 1828, for “the improved application of air to produce heat in fires, forges, and furnaces, where bellows or other blowing apparatus are required.”34 Today, we would understand this to be a process patent.
Neilson’s invention was a method for improving the efficiency of the previously existing blast furnace design. Blast furnaces are used in a process called “smelting” where fire is applied to raw metal ores to produce industrial metals. The “blast” refers to the air supplied to the fire to increase the temperature of the fire and thus allow the smelting process to occur.
In previous designs, the bellows would blast room-temperature air (called a “cold blast”) into the furnace. At the time, practitioners believed that cold air would produce a hotter furnace than hot air because experience showed that blast furnaces operated naturally at their hottest temperatures during the winter months. It was clear that the winter air produced a hotter furnace, but it was not clear why. Ironmasters attributed this effect to the coldness of the winter air. It turns out that the dryness of the winter air, not the coldness, produced a hotter furnace, but this was not known at the time.35
In the backdrop of this scientific misunderstanding, Neilson’s invention was to preheat the air before blasting, thus creating a “hot blast,” which improved the efficiency of blast furnaces by reducing the amount of fuel required to create a hot furnace.36 Neilson’s invention also constituted a scientific discovery that the coldness of the winter air was not responsible for a blast furnace’s hot temperatures in the wintertime.37 In other words, Neilson discovered a previously unknown principle that a hot blast, as a matter of physics, could create a hot flame. This combination of invention and discovery is what the English courts wrestled with in their patent eligibility analysis.
Neilson v. Harford
In Neilson v. Harford, among a litany of defenses and objections, the defendant argued that Neilson’s patent was invalid for lack of enablement and for claiming a principle.38 Regarding eligibility, the defendant argued that “it is doubtful whether the patent is for the invention of the application of hot air [a principle], or only for an improved mode of applying hot air [not a principle].”39 At trial, the jury found for the defendant on the issue of enablement and did not give a verdict on the issue of eligibility.40
The appellate court took up the case on the issue of enablement but also briefly ruled on the issue of patent eligibility.41 The entire ruling on eligibility is as follows:
It is very difficult to distinguish it from the specification of a patent for a principle, and this at first created in the minds of some of the court much difficulty . . . . We think the case must be considered as if the principle being well known, the plaintiff had first invented a mode of applying it by a mechanical apparatus to furnaces; and his invention then consists in this—by interposing a receptacle for heated air between the blowing apparatus and the furnace. In this receptacle he directs the air to be heated by the application of heat externally to the receptacle, and thus he accomplishes the object of applying the blast, which was before of cold air, in a heated state to the furnace.42
In short, the court found Neilson’s patent to be for an improved mechanical apparatus that, incidentally, applied the previously unknown principle that hot blasts can produce a hotter furnace.
In its analysis, why did the court think it necessary that “the case must be considered as if the principle [is] well known”? Why was this legal fiction necessary? Although the court did not provide any citations, I believe the court adopted this fiction in order to shoehorn the facts at hand into the previously existing case law. Recall that in Minter, the court construed Minter’s patent to be a new application of a previously known principle (specifically, the principle of leverage as applied in the design of a reclining chair). But here, in Neilson, there is an application of a previously unknown principle (specifically, the principle that hot blasts can produce a hot furnace, as applied in the design of a blast furnace). The court faced the legal problem of whether the “knownness” or “unknownness” of the underlying principle affected the patent eligibility of the mode of applying such principle. It seems that the Neilson court ruled, indirectly, that the patent eligibility of an application of a principle does not depend on whether the underlying principle was previously known or unknown.
In its § 101 case law, the U.S. Supreme Court has cited the above paragraph more than any other in English case law.43 However, in Parker v. Flook, the Supreme Court stated that Neilson stood for the proposition that all underlying principles of a claimed invention must be assumed to be previously known or, in today’s language, in the prior art.44 As we see here, Neilson does not stand for this proposition. Neilson states that it is irrelevant whether the underlying principles were known or unknown. Thus, it is not necessary for the court to identify the principles contained in a claim and “place” the principles in the prior art.45
Househill Coal & Iron Co. v. Neilson
The same Neilson patent was at issue in Househill Coal & Iron Co. v. Neilson.46 In the trial judge’s instructions, the judge, referring to Minter v. Wells, stated that the issue of patent eligibility did not depend on whether the underlying principle of the invention was previously known or unknown. All that mattered was the eligibility of the mode of application.47 This is the same as the law stated in Neilson above. The jury ruled in favor of the plaintiff, thus indirectly ruling that the patent was valid.
On appeal, the House of Lords affirmed the judgment, and thus indirectly affirmed the trial judge’s statement of law.48 This ruling by the House of Lords was the highest authority on the English law of patent eligibility that existed during the early years of U.S. patent jurisprudence.
A Restatement of English Law on Patent-Eligible Subject Matter
Given that the House of Lords affirmed the judgments of Househill, the judge’s instructions from Househill seem to provide a thorough “restatement” of the English common law on patent eligibility. The relevant portion of the judge’s instructions is reproduced below.
It is quite true that a patent cannot be taken out solely for an abstract philosophical principle—for instance, for any law of nature, or any property of matter, apart from any mode of turning it to account in the practical operations of manufacture, or the business, and arts, and utilities of life. The mere discovery of such a principle is not an invention, in the patent law sense of the term. Stating such a principle in a patent may be a promulgation of the principle, but it is no application of the principle to any practical purpose. And without that application of the principle to a practical object and end, and without the application of it to human industry, or to the purposes of human enjoyment, a person cannot in the abstract appropriate a principle to himself. But a patent will be good, though the subject of the patent consists in the discovery of a great, general, and most comprehensive principle in science or law of nature, if that principle is by the specification applied to any special purpose, so as thereby to effectuate a practical result and benefit not previously attained.
The main merit, the most important part of the invention, may consist in the conception of the original idea—in the discovery of the principle in science, or of the law of nature, stated in the patent, and little or no pains may have been taken in working out the best manner and mode of the application of the principle to the purpose set forth in the patent. But still, if the principle is stated to be applicable to any special purpose, so as to produce any result previously unknown, in the way and for the objects described, the patent is good. It is no longer an abstract principle. It comes to be a principle turned to account, to a practical object, and applied to a special result. It becomes, then, not an abstract principle, which means a principle considered apart from any special purpose or practical operation, but the discovery and statement of a principle for a special purpose, that is, a practical invention, a mode of carrying a principle into effect. That such is the law, if a well-known principle is applied for the first time to produce a practical result for a special purpose, has never been disputed. It would be very strange and unjust to refuse the same legal effect, when the inventor has the additional merit of discovering the principle as well as its application to a practical object. The instant that the principle, although discovered for the first time, is stated, in actual application to, and as the agent of, producing a certain specified effect, it is no longer an abstract principle, it is then clothed with the language of practical application, and receives the impress of tangible direction to the actual business of human life.49
Today, the most recent test from the U.S. Supreme Court on patent-eligible subject matter is the Mayo/Alice two-step test. First, one must determine whether the claim at issue is “directed to” a patent-ineligible concept. Second, one must determine whether the claim’s elements, considered both individually and as an ordered combination, embody an “inventive concept” that amounts to more than a patent-ineligible concept. Often, this analysis turns on the meaning and application of the phrases “directed to” and “inventive concept.”
On its face, this two-step test appears different from, and more cumbersome than, the old English and British case law on patent eligibility. Perhaps a simpler test would be something along the lines of (1) identify a fundamental scientific principle that is the subject matter of the claim, and (2) determine if the claim covers all practical uses of that fundamental scientific principle. Perhaps this also would agree with early U.S. case law such as O’Reilly v. Morse (1853).50
Mark Twain is reputed to have said, “History doesn’t repeat itself, but it often rhymes.” This appears to be the case in the law of patent-eligible subject matter. The Anglo-American jurists of the distant past dealt with issues that rhyme with today’s issues. Perhaps it would behoove the patent bar to look to the past for solutions to today’s issues. “What has been will be again, what has been done will be done again; there is nothing new under the sun.”51
1. Judge Dyk’s concurrence in In re Bilski, 545 F.3d 943, 966–76 (Fed. Cir. 2008), provides a summary of the history of U.S. patent law on this point.
2. 35 U.S.C. § 101.
3. Alice Corp. Pty. Ltd. v. CLS Bank Int’l, 134 S. Ct. 2347, 2354 (2014) (citation omitted).
4. Bilski v. Kappos, 561 U.S. 593, 601–02 (2010).
5. See Funk Bros. Seed Co. v. Kalo Inoculant Co., 333 U.S. 127 (1948); Gottschalk v. Benson, 409 U.S. 63 (1972); Parker v. Flook, 437 U.S. 584 (1978); Diamond v. Chakrabarty, 447 U.S. 303 (1980); Diamond v. Diehr, 450 U.S. 175 (1981); J.E.M. Ag Supply, Inc. v. Pioneer Hi-Bred Int’l, Inc., 534 U.S. 124 (2001); Bilski, 561 U.S. 593; Mayo Collaborative Servs. v. Prometheus Labs., Inc., 566 U.S. 66 (2012); Ass’n for Molecular Pathology v. Myriad Genetics, Inc., 569 U.S. 576 (2013); Alice, 134 S. Ct. 2347.
6. Flook, 437 U.S. at 592.
7. See, e.g., Markman v. Westview Instruments, Inc., 517 U.S. 370, 379–82 (1996).
8. See In re Bilski, 545 F.3d 943, 967–68 (Fed. Cir. 2008) (Dyk, J., concurring).
9. See id. at 966–76.
10. Note that the Parliament of England and the Parliament of Scotland did not merge into the Parliament of Great Britain until 1707. The Statute of Monopolies was in effect by the time of this merger.
11. The Statute of Monopolies (1624), 21 Jac. 1, c. 3, reprinted in Web. Pat. Cas. 29, 31 (sections V and VI) (emphasis added). “Web. Pat. Cas.” refers to the English law reporter Reports and Notes of Cases on Letters Patent for Inventions (1844) by Thomas Webster.
12. See, e.g., Shell Oil Co. v. Comm’r of Patents,  2 S.C.R. 536, paras. 29–34 (Can.); Anaesthetic Supplies Pty Ltd v. Rescare Ltd (1994) 50 FCR 1 (Austl.).
13. See, e.g., Househill Coal & Iron Co. v. Neilson (1843), Web. Pat. Cas. 673, 718 (HL) (declining to award attorney fees even though the litigation was “attended with great expense”).
14. For an exhaustive study of the old English case law on patentability, see Helen Gubby, Developing a Legal Paradigm for Patents (2012); and N. Scott Pierce, Patent Eligibility as a Function of New Use, Aggregation, and Preemption through Application of Principle, 23 Rich. J.L. & Tech. 11 (2017), http://jolt.richmond.edu/2017/05/19/volume23_issue4_pierce/.
15. See Hornblower v. Boulton (1799), 8 T.R. 95, 99 (KB) (“I have great respect for the contrary opinions that were given in the Common Pleas; and, probably, if I had been called upon on a sudden to determine this case, I should have been at a loss how to decide . . . .”); see also Neilson v. Harford (1841), Web. Pat. Cas. 273, 371 (“It is very difficult to distinguish it from the specification of a patent for a principle, and this at first created in the minds of some of the court much difficulty . . . .”). “T.R.” refers to Term Reports in the Court of King’s Bench (1817) by Charles Durnford and Edward Hyde East.
16. Boulton v. Bull (1795), 2 H.BL. 463, 463–64 (CP) (split decision); see also Hornblower, 8 T.R. at 97 n.(a) (unanimous decision). “H.BL.” refers to Reports of Cases Argued and Determined in the Courts of Common Pleas and Exchequer Chamber (1796) by Henry Blackstone.
17. See Hornblower, 8 T.R. at 96 n.(a) (second, third, and fifth elements).
18. See Boulton, 2 H.BL. at 463, 467; Hornblower, 8 T.R. at 95, 96 n.(a), 98 (“My method of lessening the consumption of steam, and, consequently, fuel in fire engines, consists of the following principles: . . . .” (emphasis added)).
19. See 2 H.BL. at 478–79 (Rooke, J.), 481–83 (Heath, J.), 484–88 (Buller, J.), 492, 495–96 (Eyre, C.J.).
20. See id. at 491 (“Patent rights are nowhere that I can find accurately discussed in our books.”).
21. See id. at 500 (Rooke, J., and Eyre, C.J., in favor of the plaintiff; Heath, J., and Buller, J., for the defendant).
22. 8 T.R. 95.
23. See id. at 98.
24. See id. at 99 (Lord Kenyon, C.J., and Ashhurst, J.), 101–02 (Grose, J.), 106 (Lawrence, J.).
25. See id. at 98 (Lord Kenyon, C.J.) (“The principal objection made to this patent . . . is that it is a patent for a philosophical principle only, neither organized or capable of being organized; and if the objection were well founded in fact, it would be decisive . . . .”).
26. Minter’s Patent (1830), Web. Pat. Cas. 126, 126.
28. Minter v. Wells (1834), Web. Pat. Cas. 134, 135 (motion for nonsuit).
29. Id. at 134.
31. Id. at 135 (Lord Lyndhurst, C.B.).
34. Neilson’s Patent (1828), Web. Pat. Cas. 273, 273.
35. Craig L. Bartholomew & Lance E. Metz, The Anthracite Iron Industry of the Lehigh Valley 15–16 (1988).
36. See Neilson’s Patent, Web. Pat. Cas. at 273.
37. Neilson, who was a gasworks manager rather than an ironmaster, was approached in 1825 by the manager of the Muirkirk Ironworks with the task of improving the efficiency of a blast furnace at the ironworks. It was during this task that Neilson postulated the idea of the hot blast. Neilson tried this idea on other furnaces until he perfected the design and secured a patent in 1829. See Bartholomew & Metz, supra note 35, at 16.
38. Neilson v. Harford (1841), Web. Pat. Cas. 295, 296, 369–70.
39. Id. at 296 (emphasis added).
40. Id. at 371.
41. See id. at 370–71.
42. Id. at 371 (emphasis added).
43. See Mayo Collaborative Servs. v. Prometheus Labs., Inc., 132 S. Ct. 1289, 1300 (2012); Parker v. Flook, 437 U.S. 584, 592 (1978); Boyden Power-Brake Co. v. Westinghouse, 170 U.S. 537, 578 (1898); Tilghman v. Proctor, 102 U.S. 707, 724 (1880); O’Reilly v. Morse, 56 U.S. 62, 115 (1853).
44. See Flook, 437 U.S. at 592.
45. As a side note, the Flook dissent strongly disagreed with the majority’s analysis, stating that it was inappropriate to assume that the principles were in the prior art because such analysis improperly imported § 102 and § 103 considerations into the § 101 analysis.
46. Househill Coal & Iron Co. v. Neilson (1843), Web. Pat. Cas. 673, 686.
47. The court did not explicitly cite the case name Minter v. Wells, but instead referred to it as “a case as to the application of that familiar principle the lever to the construction of chairs.” See id. at 685–86.
48. Id. at 717.
49. Id. at 683–84 (emphasis added).
50. See Scott F. Partridge, An Unacceptable Threat to Startups and Innovators from Our Patent System, 10 Landslide, no. 6, July/Aug. 2018, at 1.
51. Ecclesiastes 1:9 (New International Version).