The Federal Circuit has now had enough opportunity to address Mayo’s “well-understood, routine, conventional” test that we should have a good understanding of it. We don’t (or at least I don’t).

To begin with, the Federal Circuit cases don’t seem to differentiate among these terms. The cases also universally connect the three terms with “and” rather than “or,” but curiously most of the cases don’t seem to actually require all three to be explicitly met for a determination of ineligibility. See, e.g., Content Extraction, where the Federal Circuit noted only that the patent owner had conceded one function as being “routine.” Finally, there seems to be real disagreement about the extent to which these terms address facts as opposed to legal standards. In this post, I’m not going to comprehensively analyze all these issues, but instead will focus primarily on what these common terms mean.

The Mayo Take

Mayo didn’t provide any special definition of these three terms, and Alice’s brief mention of them was just that—a mention. There’s some indication now from Berkheimer that, “Whether a particular technology is well-understood, routine, and conventional goes beyond what was simply known in the prior art. The mere fact that something is disclosed in a piece of prior art, for example, does not mean it was well-understood, routine, and conventional.” And the court in Exergen similarly observed on the same point that, “There are many obscure references that nonetheless qualify as prior art” (citing a single copy of a German-language thesis in a German university library). But those statements hardly provide a definition, so let’s dig in a bit.

“Well Understood”

A dictionary search for “well-understood” yields only a modicum of assistance, with most definitions using the words “understood,” “known” or “comprehended,” prefaced by an adverb such as “widely,” “thoroughly” or “sufficiently.” Some definitions contrast with terms such as “half-understood” and others explain that each of two antonyms “poorly understood” and “little/not well understood” conveys different concepts. This last point is particularly instructive, since there is a significant difference between something that many people understand incorrectly (e.g., whether you can warm up a cold room more quickly by turning the thermostat up to 80 degrees rather than 70) and something that relatively few people understand (relativity, perhaps). One can readily imagine cases where this distinction could be determinative of whether a concept is “well-understood.”


The word “routine” has a very different meaning. We routinely take advantage of gravity even though its details are arguably not well-understood. While some definitions of “routine” focus on the “commonplace” aspect (i.e., something that we are used to seeing, doing, etc.), other connotations of the word emphasize the unvarying nature of the routine thing. In other words, one sense of “routine” is that it happens often while another is that it’s the same every time it happens. Again, this term provides plenty of wiggle room for a court or a patent examiner to take a result-oriented approach to section 101 analysis.


We turn now to “conventional.” Typical definitions for this word vary greatly, from something that is merely “common” or “ordinary” to that which is most common (i.e., the prevailing, standard or preferred thing). Those are very different meanings. Are metric system measurements “conventional” in the U.S.? How about in U.S. collegiate track and field? Note that the NCAA running events are now defined exclusively using metric distances and have been so defined since the 1970s, though some schools kept traditional races such as the 4x440 relay for decades after that. It doesn’t take too much imagination to conjure situations in which patent-eligibility could turn on such distinctions.

Ariosa, Exergen and Aatrix

I am not the first to voice concern about the “W-URC” test from Mayo. Indeed, Judge Linn’s concurrence in Ariosa showed an even deeper worry. Judge Linn concurred “only because I am bound by the sweeping language of the test set out in Mayo…. In my view, the breadth of the [W-URC] part of the test was unnecessary.”

Likewise, the majority opinion in Exergen noted that the district court in that case found the W-URC issue to be a “close question” and distinguished Ariosa and Mayo, where there was no such dispute in this regard. Judge Hughes, dissenting in Exergen, reached the opposite conclusion and would have held that the district court clearly erred in its conclusion from the W-URC test, applying it more broadly than the district court did. The district court applied the test to detection of arterial temperature beneath the skin, which Judge Hughes viewed as going beyond the claim elements and considering instead how those elements were used.

And in Aatrix, Judge Reyna wrote in dissent that even delving into such factual inquiries violated the court’s precedent that the § 101 inquiry is a legal one. Judge Reyna did not go on to explain how he would propose that a court might determine whether certain subject matter is W-RUC without considering facts.

Validity of Many Patents Could Hinge on Definitions

So the definitional issue is only one part of the ongoing concern about the W-URC test. Much more will undoubtedly be written about how exactly the test is to be applied. But a good starting point would be to figure out exactly what is meant by the terms “well-understood,” “routine” and “conventional.” The MPEP has an entire section (2106(05)(d)) devoted to W-URC without attempting to define each of these individual terms and differentiate among them. The validity of thousands of patents could well be determined by exactly what those three terms mean, so the task should not be ignored or taken lightly.