Key Takeaways

  • Parker v. Flook (1978) established that mathematical algorithms alone are not patentable unless applied with an inventive concept beyond conventional steps.
  • The case remains central to U.S. patent eligibility discussions under 35 U.S.C. §101, influencing later rulings such as Diamond v. Diehr, Mayo v. Prometheus, and Alice v. CLS Bank.
  • The Supreme Court in Flook held that merely implementing a formula on a computer or using it in a known process does not make it patentable.
  • Critics argue that Flook blurred the lines between §§ 101 and 103, improperly injecting “obviousness” considerations into subject-matter eligibility.
  • The decision’s continuing impact is debated, with patent scholars questioning whether Parker v. Flook remains “good law” amid modern software-patent controversies.
  • The case exemplifies the persistent “patent eligibility tangle” that courts and inventors still face when applying the abstract-idea and inventive-concept tests.

Parker v. Flook: What Is It?

Parker v. Flook was a 1978 Supreme Court case involving catalytic converters that established the basis for patenting software. It involved alarm limits on a catalytic converter in an oil refinery. 

Catalytic converters only work under certain pressures and temperatures. A catalytic converter's pressure ranges are known as alarm limits. These can change during conversion. 

Dale R. Flook came up with a method to adjust alarm limits as they changed during conversion. He filed for a patent for this method. The patent was denied because the method's only novel feature was a mathematical formula, which is not patent eligible. The appeal board of the United States Patent and Trademark Offices (USPTO) upheld this denial. 

The Court of Customs and Patent Appeals (CCPA) reversed the decision. They stated that even if the method had limited applications, this did not mean it was ineligible for patent. Eventually, the case made it to the Supreme Court. The question was whether the limited use of a formula would make a process based on the formula unavailable for patent. 

The Supreme Court upheld the initial rejection in a 6-3 decision. They determined that activity caused by a formula does not make the formula eligible for a patent unless the patent includes some other novel concept. Because formulas and algorithms exist only in the mind, they cannot be patented. 

One of the most interesting things about this case was Parker's prediction. Parker, the Acting Commissioner of Patents and Trademarks at the time, stated that should software patents be allowed, the USPTO would be flooded with "thousands of additional patent applications." As we know now, his prediction was surprisingly accurate.

Using Parker v. Flook

The Parker v. Flook decision has been very controversial. In recent years, it has been cited frequently in patent cases. This is because many people want to revisit what types of ideas and inventions are available for patent. However, the Flook decision has been maintained in the Bilski v. Kappos and Mayo v. Prometheus decisions. 

Most people find Flook to be controversial because of the idea of an inventive concept. The Flook decisions stated that an inventive application of a formula could be patented. However, the discovery of a previously unknown formula is not available for patent. This is one of the reasons filing for a software patent is very difficult. 

Between 1996 and 2012, Parker v. Flook was cited more than 140 times. 

The Flook Application

Understanding the Flook decision is easier if you look at the patent filed by Daniel R. Flook. The patent was titled Method for Updating Alarm Limits. Flook based his method of updating alarm limits during conversion on a three-step process:

  1. Measurement of the temperature process variable
  2. Using a mathematical formula to calculate a new limit
  3. Changing the alarm limit 

The difference between Flook's method and previous methods was the formula used in the second step. His patent application included the new formula. The disclosure showed that the formula's primary use was for computerized calculations. However, Flook also included several other possible uses of the formula. 

The patent examiner decided that patenting Flook's formula would also patent the underlying mathematics. As we know, math processes are not eligible for patent. 

The CCPA's Reasoning

Unlike the Patent Appeal Board and later the Supreme Court, the CCPA decided in Flook's favor. They did so using a narrow interpretation of In re Christensen, where it only applied to processes in which no additional steps were required to use an algorithm. Because Flook's formula was the second step in a three-step process, and the formula resulted in an activity after it was solved, it was ruled a method and was patentable. 

The Supreme Court's Logic

Ultimately, the Supreme Court decided Flook's method could not be patented under 35 U.S.C. §101 rules. The court stated that Flook's patent was a discovery involving the laws of nature. This makes it non-patentable. This idea was established in the Benson case. 

Flook tried to argue that his formula resulted in a post-solution activity: the changing of the alarm limit. He claimed that this made his patent different from the one in the Benson case. The Court disagreed and stated his patent counted as prior art. This was because the process of catalytic conversion was already established and well-known. 

A later Supreme Court case known as Diamond v. Diehr was long assumed to overturn the Flook decision based on desuetude, or disuse. However, the later Mayo case resolved conflicts between these two decisions. 

Broader Implications of Parker v. Flook

The Parker v. Flook decision remains one of the most debated rulings in patent law because it refined how courts interpret 35 U.S.C. § 101, the statutory basis for patent eligibility. The Court ruled that even if a mathematical formula or algorithm produces a practical result, it cannot be patented unless the claim includes an inventive application that transforms it into something more than an abstract idea. This reasoning built on Gottschalk v. Benson (1972) and was later contrasted with Diamond v. Diehr (1981), which upheld a patent involving a computer-controlled rubber-curing process.

In Flook, the Court viewed the formula for updating catalytic-converter alarm limits as akin to a law of nature—discoverable, but not patentable. It emphasized that “post-solution activity” such as changing the alarm setting did not transform an unpatentable formula into a patentable process. This established the modern foundation for the abstract-idea exception used in later decisions like Bilski v. Kappos and Alice v. CLS Bank.

The Flook opinion’s analytical framework—separating mathematical formulas and natural laws from their applications—has influenced courts to focus on whether a claim adds “something more,” an inventive concept beyond mere automation. This framework became integral to the two-step Mayo/Alice test now used in evaluating software and biotech patents.

History of Software Patents

A problem with software patents is that their interpretation has largely been left to the courts. The government's legislative branch has resisted clarifying the subject. The Manual of Patent Examination and Procedure has been the executive branch's only guidance on software patents. 

Three Supreme Court rulings have been related to software patents:

  • Gottshalk v. Benson
  • Parker v. Flook
  • Diamond v. Diehr 

The Benson and Flook decisions definitively stated that software cannot be patented, even if it is useful and there is a last step that is physical in nature. The Diehr decision upheld a patent on a piece of complex machinery. This has generally been seen as the basis for the definition of a general-purpose computer. 

The Diehr case involved a process for creating vulcanized rubber. The court ruled that because the formula involved in the process was used to change the state of the rubber, it constituted an actual machine. This made it available for patent. 

The Alappat decision used Diehr as a basis. It argued that applying software to a stock computer would create an entirely new machine. This removed the distinction between a general-purpose computer and a specialized device, resulting in all pieces of software being eligible for patenting. 

Flook Criticism

There has been much criticism of the Flook decision. In 1979, the CCPA reached a decision in re Bergy. A CCPA judge, Judge Giles, condemned the Flook decision. One of the reasons was that the Supreme Court had recently overturned a previous Bergy decision and instructed the CCPA to re-examine the issue based on the Flook decision. 

Giles stated that the Flook decision did not give the guidance that the Supreme Court believed. He also said that Flook wrongly combined provisions in Section 101 and Section 103 of the Patent Code. He stated that the Court incorrectly used Section 101 to make its decision. He believed that Section 101 was never meant to define patentability. This was reserved for Sections 102 and 103. 

Giles believed that the only thing to consider for patent eligibility is if the invention is useful, novel, and non-obvious. He did not agree that using a natural principle must be inventive to be eligible for a patent. However, Giles overlooked part of the Flook decision. Flook only claimed to use his formula in a conventional way. This meant it was neither new nor non-obvious, two of the main requirements for a patent. 

Flook's admission that he did not use his formula in an inventive way made the ruling easy. This will likely not be the case for other patents involving natural processes. This limits how the Flook decision can be used to determine eligibility, which was Giles' point in his criticism. 

Is Parker v. Flook Still Good Law?

More than forty years after its decision, Parker v. Flook continues to shape the debate over patent-eligible subject matter. Some commentators argue that Flook has been partially eclipsed by Diamond v. Diehr, which many see as limiting Flook’s reach by emphasizing the importance of the overall process rather than isolating a formula. Yet the Supreme Court has never explicitly overturned Flook, and modern cases such as Mayo v. Prometheus (2012) and Alice v. CLS Bank (2014) echo its reasoning.

Legal scholars, including those writing for Patently-O and The IP Law Blog, note that Flook serves as a judicial anchor for the idea that laws of nature, natural phenomena, and abstract ideas remain outside patentable subject matter. They observe that the Federal Circuit and district courts still cite Flook when rejecting algorithm-based or data-processing claims that lack a novel technological implementation.

However, critics contend that the decision’s logic muddles the line between patent eligibility and patentability. By requiring an “inventive concept” within § 101 analysis, Flook arguably introduces considerations meant for §§ 102 and 103—novelty and non-obviousness—into a threshold eligibility inquiry. This blending has created ongoing inconsistency, leading many attorneys and inventors to describe the modern patent landscape as a “tangle” of conflicting interpretations.

Some modern commentators suggest that Flook remains a cautionary precedent rather than a definitive rule. While the case clarified that abstract ideas alone are not patentable, its application is now intertwined with Mayo and Alice, which together guide today’s analysis under § 101. As Patently-O observed, whether Parker v. Flook “is still good law” depends less on its formal status and more on how courts continue to apply its reasoning to evolving technologies.

Economic Concepts Implemented By Computers

In 2014, the Supreme Court ruled on a hotly contested case between CLS Bank/CLS Services and Alice Corporation. It centered on how Section 101 of the patent code applied to computer-implemented inventions. In the ruling, the Court decided that computer-implemented inventions must compare to Section 101 in two steps:

  1. If the patent is an abstract idea, such as an economic practice
  2. If the patent contains an inventive step that makes it eligible for a patent

Alice's patent failed both steps, which is why the Court ruled it ineligible. 

Section 101 allows patents for people who have discovered:

  • A new or useful process
  • A machine
  • A manufacture
  • Compositions of matter
  • An improvement over any of the other items

However, there has always been an exception for abstract ideas and natural laws. This exception has been used to deny patent eligibility in the Benson, Flook, and Bilski cases. Unfortunately, this abstract exception did not establish rules for challenging patents. The Mayo decision sought to establish a framework, but judges still disagreed on how it could be applied. 

In the Alice case, Alice stated that CLS had infringed on their patents. These patents involved intermediate settlement, an economic concept that a computer used to make transaction records to facilitate an exchange. Alice stated their right to the concept in three ways:

  1. As a process for transaction settlements
  2. As the computer used to for these settlements
  3. As a media storage that contained computer programming 

CLS claimed that Alice's patents were based on an abstract idea and brought a case to a U.S. District Court. They argued Alice's patents did not disclose any computer programming and only included general ideas that could be found in any computer. The District Court ruled in CLS's favor. While the Federal Circuit initially overturned this decision, a second hearing resulted a 7-3 method/media decision and a 5-5 system decision. 

Alice requested the Supreme Court hear the case to resolve the Federal Circuit's decisions. Their contention was that intermediated settlement was not abstract. This is because it did not constitute a natural law like a mathematical formula. Alice also said they did not claim the entire concept in their patent because it required a computer to function.  

CLS argued that intermediated settlement was a fundamental economic practice and that it could not fulfill an inventive concept required for patent. 

The Supreme Court ruled unanimously in CLS's favor. Justice Thomas wrote the decision. The main point of the decision was that the necessity of a computer did not mean that intermediated settlement wasn't an abstract concept. However, the ruling did not state that all pieces of software are ineligible for patent. For instance, software that altered a computer's functioning might still be patentable. 

The decision included a few key points:

  • Mayo's two-step test should be used for all patent challenges. The first step is whether the patent is focused on an abstract idea. The second is if the patent includes an inventive use of the abstract idea.
  • The Mayo test was applied to Alice patents, which failed both steps.
  • Generic use of a computer cannot make an abstract idea eligible for patent.
  • The Diehr decision was not applicable because that decision involved an abstract idea that transformed an existing process. Alice's patents did not alter the functioning of the computer in question.
  • The computer's physical nature was irrelevant, and treating it as relevant would allow anyone to patent a natural process so long as a computer system was involved. 

The Alice decision's straightforward nature supports the rules established by the Bilski case. Business method patents will often be found ineligible under Section 101 rules. The use of a computer does not make an abstract concept patentable unless an inventive concept is present. 

Continuing Relevance of Flook in Modern Patent Law

In today’s patent landscape, Parker v. Flook underpins the tension between protecting innovation and preventing monopolies on abstract ideas. The decision’s principles reappear in Alice v. CLS Bank and Mayo v. Prometheus, both of which reaffirm that claims directed to fundamental ideas or natural laws must contain significant inventive elements to be patent-eligible.

This issue remains critical as courts confront software, AI, and financial-technology patents. Judges continue to cite Flook when distinguishing between inventions that use computers as tools and those that truly improve computer functionality. For example, post-Alice cases have invoked Flook to invalidate patents on data-processing or risk-management methods that lacked a transformative technical contribution.

The ongoing relevance of Flook demonstrates that patent-eligibility law still lacks bright-line rules. Commentators, including those from The IP Law Blog, describe the current situation as a “patent-eligibility tangle” that leaves inventors, investors, and practitioners uncertain about how courts will treat algorithmic inventions.

For those developing software or technology-driven processes, understanding Parker v. Flook remains essential. It highlights the importance of drafting patent claims that integrate algorithms into inventive, concrete applications—something that continues to challenge innovators navigating § 101 jurisprudence.

Frequently Asked Questions

  1. What was the central issue in Parker v. Flook?
    The main issue was whether a mathematical formula used to update alarm limits in catalytic conversion could be patented. The Supreme Court held it could not, as formulas alone are not patent-eligible.
  2. How did Parker v. Flook influence later patent cases?
    It set a foundation for the abstract-idea doctrine later applied in Mayo v. Prometheus and Alice v. CLS Bank, shaping the modern two-step test for patent eligibility.
  3. Did Diamond v. Diehr overturn Flook?
    No. Diehr limited Flook by emphasizing that a process using a formula can be patentable if it results in a physical transformation or inventive application, but it did not overturn Flook.
  4. Why is Parker v. Flook controversial?
    Critics argue it conflates patent eligibility with novelty and obviousness tests, creating ongoing ambiguity in determining which inventions qualify under § 101.
  5. Does Parker v. Flook still apply today?
    Yes, it remains an influential precedent in software and biotech patent cases, serving as a touchstone for evaluating algorithm-based inventions.

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