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Be Careful Claiming Trees in the Middle of the Forest—and Be Sure You Win on a Dispositive Issue

Although both parts of 35 U.S.C. § 112, written description and enablement are distinct requirements that a patent specification must meet.

The written description is an issue of fact. To meet the written description requirement, a patent specification must describe the invention sufficiently so that one of ordinary skill in the art would understand that, according to some recent case law, the inventor was in possession of the claimed subject matter.

Enablement, on the other hand, is a question of law based on underlying factual findings. To meet the enablement requirement, according to somewhat older case law, a patent specification must teach one of ordinary skill in the art how to make and use the invention without undue experimentation.

Both the written description requirement and the enablement requirement are found within 35 U.S.C. § 112, but the Federal Circuit has repeatedly held they are two separate requirements. In other words, it is necessary to meet both requirements; meeting the written description requirement does not guarantee that the enablement requirement has been met and vice versa.

It is well known that prior art must meet the enablement requirement to qualify as prior art for purposes of 35 U.S.C. §§ 102 and 103. Just as patent specifications must meet both written description and enablement requirements, however, prior art may also be required to meet something akin to the written description requirement.


In Ex parte Hassler et al., Appeal No. 2020-001367 (P.T.A.B. Nov. 13, 2020), the Board reversed the Examiner’s obviousness rejections. The patent applicant appealed, arguing that it was entitled to priority dates effective to antedate the primary reference. Because its claims lacked written description, it lost on those arguments. However, the Board credited Appellant’s arguments that the prior art relied on by the USPTO was simply insufficient to provide a reasonable expectation of success to support the obviousness rejections.


Appellant appealed to the Board from the Examiner’s Final Rejection of many claims of its Application No. 13/433,097 (“the ’097 Application”). The ’097 Application is directed to the use of rare-earth-containing additives comprising rare earths of plural oxidation states to remove non-metal-containing contaminants from drinking water and aqueous streams.

In his Final Rejection, the Examiner determined that many claims of the ’097 Application were obvious over combinations of the prior art references identified as, inter alia, Fischmann and McNew.

Claim 1 of the ’097 Application recites (with emphasis added):

  1. A method, comprising:

(a) receiving an oxyanion-containing water, the oxyanion-containing water comprising at least one non-metal-containing oxyanion, wherein the at least one non-metal-containing oxyanion comprises one or more of hypophalite (XO-), hypochlorite (ClO-), hypobromite (BrO-), hypoidite (IO-), halites (OXO-), chlorite (OClO-), bromite (OBrO-), halite (XO3-), chlorate (ClO3-), bromate (BrO3-), iodate (OI3-), perhalates (XO4-), perchlorate (ClO4-), perbromate (BrO4-), periodate (IO4-, IO64-, I2+nO10+4n(6+n)-, where n is positive integer greater than zero), sulfurous (SO32-), disulfurous (S2O52-), thiosulfate (S2O32-), dithionite (S2O42-), polythionate (SnO62-), peroxodisulfate (S2O82-), disulfate (S2O72-), trisulfate (S3O102-), tetrasulfate (S4O132-), and pentasulfate (S5O162-); and

(b) after step (a), contacting the oxyanion-containing water with a separate component comprising a rare earth to remove more than 50% of the oxyanions from the oxyanion containing water.

Obviousness Rejection

The Examiner determined that Fischmann taught both oxyanion-containing aqueous streams comprising hypochlorite or persulfate and contacting the oxyanion-containing stream with a separate composition to remove substantially all of the oxyanions from the oxyanion-containing stream, processes corresponding to the two steps of claim 1. However, the Examiner found that Fischmann did not teach that this separate composition contained a rare-earth element.

That rare-earth element could be found, in the Examiner’s view, from McNew, which disclosed a process that uses the rare earth element cerium (Ce), instead of conventional sorbents, to remove oxyanions from aqueous streams.

Based on Fischmann and McNew, the Examiner concluded that it would have been obvious to combine Fischmann’s process with McNew’s use of cerium. In the Examiner’s view, this combination would have had the added benefit of additional absorption of toxic materials from industrial waters, and it would have provided “predictable results.” Id.

On appeal, the patent applicant argued that Fischmann did not constitute prior art. Even if it did, the Appellant argued, the Examiner’s statements regarding McNew’s composition and its use in the dichlorination process taught by Fischmann were improper and insufficient to establish obviousness.

Written Description v. Enablement Issues

Appellant argued that the obviousness rejections were improper because they failed to account for the ’097 Application’s claimed priority date. The ’097 Application claimed priority to U.S. Patent Application No. 2011/0309017 (Hassler). Hassler itself claimed priority to two provisional applications: US 61/323,758 (“the ’758 provisional”) and US 61/325,996 (“the ’996 provisional”) (collectively “the Hassler provisional applications”).  

The Examiner determined that the Hassler provisional applications did not meet the written description requirement. In particular, the Examiner found that the Hassler provisional applications did not disclose any species of non-metal oxyanions other than selenium (Se). In the Examiner’s view, the Hassler provisional applications did not disclose all of the Markush elements recited in claim 1 of the ’097 Application.

Appellant argued that while the Hassler provisional applications failed to expressly disclose the particular Markush species, they did disclose a genus of oxyanions generally. Appellant further argued that even though the Hassler provisional applications did not define non-metal oxyanions other than selenium oxyanions as “target-material containing,” this did not limit the scope of the genus “oxyanions.” More generally, the Appellant argued that under 35 U.S.C. § 112, it is not necessary to disclose in detail what was conventional or well-known to one of ordinary skill in the art.

The Board’s Decision

On appeal, the Board found Appellant’s priority arguments unpersuasive. While a specification does not necessarily need to disclose what is well-known and conventional to satisfy the enablement prong of 35 U.S.C. § 112, the Board noted that written description is a separate requirement. And, according to the Board, that separate written description requirement was not met by the ’097 Application.

The Board emphasized that whether oxyanions, as a class, were well-known to one of ordinary skill did not address whether the Hassler provisional applications provided sufficient written description support to establish a claim of priority for the claimed invention.

The Board noted, citing Purdue Pharma L.P. v. Faulding Inc., 230 F.3d 1320, 1326 (Fed. Cir. 2000), that “[i]t is well settled that one cannot disclose a forest in the original application, and then later pick a tree out of the forest and say here is my invention.” Rather, to comply with the written description requirement, an applicant must convey with reasonable clarity to those skilled in the art that they were in possession of the claimed invention as of the filing date.

The Board further emphasized this point, finding the specification must provide some guides (or, as the Board put it, “blaze marks”) that disclose the claimed invention “specifically as something appellants actually invented.”

Therefore, while the Hassler provisional applications complied with 35 U.S.C. § 112’s enablement requirement, they did not comply with its written description requirement. The Board thus held that the Appellant did not sufficiently demonstrate that any reference relied upon for priority conveyed that the inventor was in possession of all the claimed Markush species. Thus, the Appellant did not establish that the present application could antedate Fischmann.

Obviousness Issues

Even without that earlier priority date, all was not lost for the Appellant, as the Board ultimately reversed the obviousness rejections of all claims at issue.

Specifically, the Board held that it would not have been obvious to the skilled artisan to substitute McNew’s rare-earth compositions for Fischmann’s activated-carbon sorbent, even though McNew expressly disclosed oxyanions broadly. Rather, McNew disclosed no examples using the disclosed rare earth composition to sorb non-metal oxyanions. There was no evidence or technical reasoning to provide sufficient basis for the skilled artisan to reasonably expect that McNew’s rare-earth compositions would adequately sorb non-metal oxyanions. Regarding the Examiner’s other obviousness rejections, the Board likewise concluded that they suffered from the same deficiencies as the Examiner’s combination of Fischmann and McNew.  


When drafting a patent specification, it is important to remember that enablement and written description are two separate requirements. While enablement does not require that an applicant disclose in detail that which is well-known or ordinary to one of skill in the art, it does demand that the specification teach one in the art enough to make and use the invention without “undue experimentation.”

On the other hand, written description requires, according to this Board decision, that the disclosure, as seen by one of ordinary skill in the art, demonstrate that the applicant was in possession of the claimed invention. Exercising best efforts to ensure that a patent specification complies with both requirements will help mitigate potential issues. 

Also, a thoughtful applicant must consider claims which are sufficiently narrow to pass muster in a priority argument based on both written description and enablement, while balancing the claims’ scope with the likelihood of infringement. If infringement seems unlikely because the narrow claims are too easy to design around, the applicant may consider including at least some means-plus-function claims. For some examples, see U.S. Patent Nos. 8,722,872, 9,149,464, and 10,413,611, all pharmaceutical composition patents utilizing at least some means-plus-function claim language.[1]

Finally, the applicant should take heart from the logic and holding of Hassler—losing a priority date argument does not mean all is lost. Substantive arguments against the rejection may remain. Clearly, a detailed, compelling argument of lack of sufficient basis for a reasonable expectation of success can still preserve a patent, even when the applicant cannot prevail on priority arguments.

[1] See U.S. Patent 8,722,872, Claim 9 (“A pharmaceutical composition comprising (a) means for reducing the amount of active hsp27 in cancerous cells and (b) a pharmaceutically acceptable carrier.”); U.S. Patent No. 9,149,464, Claim 13 (“A pharmaceutical composition, comprising (a) [compound], and (b) a means for increasing the circulation time of the compound in an aqueous environment.”); U.S. Patent No. 10,413,611, Claim 1 (“A pharmaceutical composition comprising: (a) at least one poloxamer…and (b) means for keeping the pharmaceutical composition in liquid phase up to a temperature of about 40° C in vitro, wherein the pharmaceutical composition is used…”).

© 2021 Finnegan, Henderson, Farabow, Garrett & Dunner, LLPNational Law Review, Volume XI, Number 110



About this Author


Melissa Santos, Ph.D., focuses on patent prosecution, patent litigation, and client counseling in the areas of chemicals, pharmaceuticals, and materials science. She has technical experience with polymer chemistry, fabrication and characterization of materials, and protein and genetic engineering. 

Melissa worked on patent prosecution and various aspects of patent litigation during her time as a summer associate at Finnegan. She previously served as a legal intern in the patents group at a global pharmaceutical company, conducting inventorship interviews with scientists and...

Brooke Wilner Patent Attorney Finnegan

Brooke Wilner, a registered patent attorney, enjoys a varied trial and appellate litigation practice. She practices before U.S. district courts, state courts, the Patent Trial and Appeal Board (PTAB), the U.S. Court of Appeals for the Federal Circuit (CAFC), and the U.S. International Trade Commission (ITC).

Brooke represents both patent owners and accused infringers across a broad range of mechanical and electrical technologies, including clients in the aerospace, automotive, consumer products, software, and hardware industries. She has...

Amanda Murphy IP Lawyer Finnegan

Amanda Murphy, Ph.D., focuses her practice on strategic client counseling, portfolio management, and patent prosecution for a range of clients, including small startup companies, research foundations, and large biotechnology and pharmaceutical companies.

Amanda provides patentability opinions, prepares new patent applications, prosecutes U.S. and foreign applications, and represents appellants before the Patent Trial and Appeal Board (PTAB) of the U.S. Patent and Trademark Office (USPTO). She has experience in prosecuting inter partes ...

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Thomas L. Irving Intellectual Property Finnegan, Henderson, Farabow, Garrett & Dunner Washington, DC

Tom Irving has some 45 years of experience in intellectual property law. His U.S. pharma practice includes America Invents Act (AIA) post-grant proceedings, due diligence, counseling, patent prosecution, reissue, and reexamination. In addition to advising on procuring strong U.S. patents, Tom counsels clients on a wide range of mainly pharmaceutical matters, including pre-litigation, Orange Book listings of patents covering FDA-approved drugs, infringement issues, enforceability, supplemental examination, and validity analysis. He has served as lead counsel in numerous patent interferences...