Looking Back: Graver Tank after 70 years

by Dennis Crouch

The Supreme Court’s landmark 1950 decision in Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605 (1950) is one of the court’s most cited patent cases.  The decision established important guideposts for applying the doctrine of equivalents (“DOE”), including consideration of the prior art and a focus on the substantiality of differences. While courts today emphasize evaluating equivalence on an element-by-element basis, Graver Tank‘s substantive analysis remains highly influential.

Linde Air Products held a patent on welding fluxes using alkaline earth metal silicates. US Patent No. 2,043,960. Graver Tank’s flux substituted manganese silicate, which was not an alkaline earth metal. Though Graver Tank’s flux did not literally infringe, the Court found it performed “the same work in substantially the same way [to] accomplish substantially the same result.”  This has become known as the function-way-result or tripartite test.

The decision thus reestablished that products need not infringe literally to infringe a patent. Even if the language of a claim isn’t met exactly, the doctrine of equivalents provides protection from knock-offs that are only trivially different.  An important aspect of this outcome is that its factual intensity meant allowed patentees to avoid summary judgment and instead frequently reach jury.

Over the past 70 years, Graver Tank’s doctrine of equivalents analysis has been instrumental in assessing infringement and remains a key tool for patentees to enforce their rights against insubstantial changes. At the same time, the doctrine has been further shaped and limited. Courts today emphasize an element-by-element approach rather than looking at the product as a whole. Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997). Prosecution history estoppel limits the doctrine for claims amended or argued during patent prosecution. Id, See also, Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002).  And, the doctrine of vitiation precludes a finding of equivalence when it would effectively eliminate or “vitiate” a claim limitation. See, Freedman Seating Co. v. American Seating Co., 420 F.3d 1350 (Fed. Cir. 2005) and Depuy Spine, Inc. v. Medtronic Sofamor Danek, Inc., 469 F.3d 1005 (Fed. Cir. 2006).

In Warner-Jenkinson, the Supreme Court reaffirmed the viability of the doctrine of equivalents, but placed some limitations on its application. Specifically, the Court held that the doctrine must be applied to individual elements of a claim, not to the invention as a whole. The Court also held that prosecution history estoppel can bar the doctrine of equivalents when an amendment or argument during patent prosecution surrenders subject matter that would otherwise fall under equivalents.  In Festo, the Supreme Court provided more detail on prosecution history estoppel (PHE)–establishing a a presumption against application of the doctrine of equivalents for claim limitations that were amended during patent prosecution for reasons related to patentability.

In Graver Tank, the Court had applied the doctrine to find infringement based on the substantial similarity of the overall compositions at issue. Under the standard set forth in Warner-Jenkinson, the Graver Tank analysis would likely have compared the “alkaline earth metal silicate” and “manganese silicate” elements specifically to determine their equivalence. Additionally, prosecution history estoppel may have precluded equivalence, if the reason alkaline earth metals were claimed was to overcome a rejection during patent prosecution.

The rise of these legal limitations has given judges tools to more frequently dismiss DOE claims on summary judgment or JMOL.

As the chart shows above, courts continue to cite and rely upon Graver Tank. The following are typical reasons:

  • To support application of the doctrine of equivalents generally and reference the “function-way-result.”
  • To emphasize that minor or insubstantial differences do not avoid infringement.
  • To note that equivalents is a question of fact for the jury to decide rather than a question of law.  Typically, expert testimony will provide the key underlying evidence.

On the fact/law issue, the majority opinion explains that a question is more likely to be factual in nature when it requires specific scientific knowledge. “Particularly is this so in a field where so much depends upon familiarity with specific scientific problems and principles not usually contained in the general storehouse of knowledge and experience.” Id. This quote has been cited by a number of courts in other fields when attempting to determine whether a particular issue is legal or factual.

One important note is that this post focuses on the majority opinion penned by Justice Robert Jackson.  Justices Hugo Black and William Douglas jointly wrote a dissent concluding that patents should be limited to their literal scope based upon the claim language.  The dissent argued that the DOE undermined the statutory requirement for clear patent claims.  See 35 U.S.C. 112(b) (“claims particularly pointing out and distinctly claiming”).

22 thoughts on “Looking Back: Graver Tank after 70 years

  1. 5

    I always thought it was interesting that the patent at issue in Graver Tank included an express disclosure that “[w]e have used calcium silicate and silicates of sodium, barium, iron, manganese, cobalt, magnesium, nickel and aluminum . . . in various proportions . . . While a number of these conductive welding compositions are more or less efficacious in our process, we prefer to use silicates of alkaline earth metals.” (‘960 patent at p. 2, ll. 62-72)

    If the Federal Circuit was deciding Graver Tank today, I wonder how it would have come out. See, e.g., PSC Computer Prod., Inc. v. Foxconn Int’l, Inc., 355 F.3d 1353, 1359-60 (Fed. Cir. 2004) (“Were the patentee allowed to reclaim some specifically disclosed-but-unclaimed matter under the doctrine of equivalents, the public would have no way of knowing which disclosed matter infringed and which did not . . . Such a reclamation would eviscerate the public notice function of patents and create uncertainty in the law.”).

    1. 5.2

      Thanks for that reminder of the previously noted serious spec problem of validly granting DOE on the facts in Graver Tank, but the Fed. Cir. is still stuck with it.

  2. 4

    The prior blog charting U.S. patent issuances says that “the decrease in granted patents relative to last year may be the result of a delay between allowance and publication.” On Gene’s blog it was also attributed to an increase in pending applications.

  3. 3

    With respect to the chart and Ben’s comments. Ben is right that I did go after Jason last time. (It was two years ago.) I had remembered it as only holding Lemley to account. Read my comments. They are accurate and correct. Ben: your comments do not even make sense under a logical, ethical, and moral system. I get that you are using Woke logic, which means you feel you are right, so any rhetorical tactic is justified.

    The fact that Jason feels he can’t respond to my comments is stomach turning. I think we need to seriously start considering defunding the universities and starting over. My criticisms are rational and fair. And they are accurate. I believe the way Lemley presented the data violates academic ethical standards for presenting academic papers or research. Certainly, if in my field of study had I presented a paper as Lemley did, I would have been reported to the university for a potential violation. If Lemley admits that he is an advocate for the ending patents, then fine. It is an advocacy presentation. But, it was presented as an academic paper.

    The fact that I even have to explain any of this is illustrates how terrible things are.

    >>Greg, with all due respect, you are FOS. First, the only person I clearly made “asperations against [his] ethics” is Professor Lemley who has put up a version of this chart in the past and said that it indicates the patent system is as healthy as ever and innovation is not hurt by weakening patents. Second, given the context of how this chart has been used and its implicit meaning, one can say that without further information that it is unethical to present this chart.

    >>Writ large is that the issuing patents and patent applications are being used to say everything is fine. Look at Paul’s post above. And, yet, the numbers aren’t normalized and the number of these patents that are for US inventions is not given.

    1. 3.1

      The big picture is the academics feel that patents do not fit well with their neo-Marxist utopia, so they think they do not need to be ethical in their attempts to destroy the patent system.

      Defund the universities. Start over. Mass layoff of all professors. End tax free status for private universities.

      1. 3.1.1

        And Greg the WIPO report is good but it doesn’t break down the US applications to a level where we can understand where the invention was made.


          Table B11 (pg. 55 of the 2023 report) shows that 10.3% of the national phase entries in the USPTO over the last year were from CN origin PCTs. That is not exactly the same thing as “inventions made in CN,” but it is close enough to give one a read on the growth of CN-origin inventions in the overall US mix. If one follows Table B11 from year to year, one can learn how CN is affecting the overall patent composition of the USPTO’s work.


            Not really enough. Too many applications are filed first in the US or they are filed with priority claimed from a CN application.

            I do a lot of foreign work. Plus, it is even more complicated as often what happens now with the corporation being the applicant is that corporation is a US corporation but the inventors are not in the USA.

            Frankly, I think the inventors I work with in India, China, Russia, Japan, Korea, UK, France, Ukraine, Italy, and so forth are amazing. And I think it is great way to bring the world together to have inventors from all over the world. I’ve worked with inventors from many more countries than the list above.

            But I do think we should get a picture of what is happening with inventions made in the USA.


              Yes NW, as the relative % of foreign STEM graduates and foreign R&D spending and market shares increases in comparison to the U.S. it would seem logical for the [already substantial] percentage of foreign-origin U.S. patent applications to increase.* But, where are accurate numbers, and do they distinguish inventions made in U.S. company owned labs or factories in foreign countries or otherwise U.S. owned? Have issued patent Assignment records been sampled lately?
              *But as also noted, if U.S. patents now have substantially effectively reduced value [due to unenforceability or whatever] relative to patents in other countries, that should logically be reducing foreign owned application filings in the U.S.?


                It doesn’t seem like anyone has figured out these numbers.

                I note that the wackos on the blog have tried to make it seem like I had a problem with Jason’s post this time. I didn’t. My comments were merely that we need to get a breakdown of the numbers to understand what is happening in the USA.

  4. 2

    One note. Although Graver Tank remains important, most DOE decisions no longer cite the case. For example, Westlaw shows about 170 patent decisions that mention the doctrine of equivalents, and less than 10% of those cite Graver Tank.

    1. 2.2

      Dennis, this is not the only patent law topic on which the Fed. Cir. often fails to cite any controlling Sup. Ct. case and only cites some of its own, and not necessarily the first.

  5. 1

    Interestingly, just like the chart in the immediately previous post, this chart shows a distinct and notable inflection point when the CAFC comes online. However, while it makes intuitive sense that the advent of the CAFC should affect the total number of grants each year, it is a little harder to understand why the advent of the CAFC should increase the frequency with which Graver Tank gets cited.

    Most of these citations in the count are district court judgments, right? Why would district court judges become more inclined to cite Graver Tank now that they are being reviewed by a circuit court in D.C. rather than by their regional circuit?

    1. 1.1

      This chart would be more interesting complemented by a chart showing the % of patent decisions that include a Graver Tank citation. The number of court decisions in Westlaw has increased substantially, and so the rise does not necessarily mean a proportional rise. This also makes the fall since 2000 more dramatic.

      1. 1.1.1

        Ah, got it. So maybe that big jump in the slope post-1980 reflects a growth in patent cases being filed, and with more total patent cases, there are more occasions to cite Graver Tank. That makes sense. Thanks.

    2. 1.2

      >hy would district court judges become more inclined to cite Graver Tank now that they are being reviewed by a circuit court in D.C. rather than by their regional circuit?

      It’s before my time, but as I understand it, most pre-CAFC infringement lawsuits were de-facto decided via civil procedure (forum shopping), not patent law.

    3. 1.3

      “why the advent of the CAFC should increase the frequency with which Graver Tank gets cited.”

      Probably just some internal staffer or judge (or plural) got hired on at the advent of the CAFC that likes citing that decision or thinks it’s supar important.

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