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Prosecution History Estoppel: Still Lurking for The Unwary
by: Philip Summa of Summa PLLC  -  
Tuesday, September 7, 2021

What is the current role of the Patent Attorney?  Or perhaps, what is the current value of any given patent attorney?  Does the mere possession of a patent—gold seal, ribbon, Bristol board—have intrinsic value or is more required to get commercial value?  For practitioners, can the attorney make a difference?  A June 2021 Federal Circuit decision suggests it can.

The practice of patent law has changed rapidly in parallel to the growth of the internet, processing power, and computer memory.  The public search room at Crystal City—a cross between and among a library, a FedEx Kinko’s, a WFT pep rally, and a Medieval bazaar—has moved to a quiet row of cubicles in Alexandria.  Exhaustive online searching can be contracted out efficiently, and decent search results are quickly available from major patent offices.  A word processor (or some enhanced version) can check our specifications for consistency and our claims for antecedent basis.  Our draftsmen work from software, with India Ink and Bristol Board being unknown terms from a distant past.

At a minimum, however, two roles of the patent attorney remain:  obtain the broadest possible claim scope and—my theme here—protect the prosecution history.

The recently decided Federal Circuit case of SpeedTrack, Inc. v. Amazon.com, Inc., 998 F.3d 1373 (Fed. Cir. 2021) (“SpeedTrack“), turned on one of patent law’s “ruling elders”:  prosecution history estoppel.


SpeedTrack deals with the manner in which information is stored in a computer and then retrieved from that computer.  The subject matter issued as US Patent No. 5444360 on August 6, 1996.

The claims of the ‘360 patent purport to cover a method of finding files (e.g., a particular document such as a letter) in a “data storage system” of a computer without “defining” (using) a “predefined hierarchical relationship.”  As best understood by this writer, a “predefined hierarchical relationship” is the “everything in this computer” (i.e., root) directly from which descend subdirectories, then (if desired) sub–subdirectories, etc., with the files residing in some particular subdirectory.  Perhaps not “turtles all the way down” (https://en.wikipedia.org/wiki/Turtles_all_the_way_down) but at least “lots of turtles before you find what you want.”

To replace the hierarchical relationship, the ‘360 patent describes and claims a method that creates a list of categories, with a user assigning one or more categories to a file.  To find a file, the user picks at least one category, and the system generates a list of results.  Adding categories (e.g., “memo AND infringement”) narrows the results for the user and finds the desired file.

One asserted advantage of the ‘360 method is the guarantee that—because the searcher is forced to start with a category—at least one file will always turn up.  Such is not the case when the searcher has the option of misspelling a search term rather than clicking on a category.


The application that became the ‘360 patent was originally filed on November 23, 1992, then re-filed as a continuing application on February 3, 1995.  Thus, perhaps the ‘360 patent represents the “early middle ages” of the personal computer age.

To further emphasize the distinction between the prior art (hierarchical relationships) and the claimed invention (using categories), on March 17, 1995—over 26 years before the June 3, 2021 opinion—SpeedTrack amended the claims to overcome a particular reference (Schwartz; US 5047918) and did so by adding (inter alia) the phrase “having no predefined hierarchical relationship” to the independent claims.

Stop and reflect.  An amendment offered in 1995 decides a Federal Circuit appeal in 2021 for a patent that expired in 2013.

To be fair to all concerned, the patent attorney is always constrained by the prior art and the inventor’s contributions.  Thus, adding something to the prosecution history—and thus by definition creating prosecution history estoppel—may be entirely necessary to obtain claim coverage.  “Something,” however, covers a multitude of possibilities and the possibilities range from giving away the farm (too-narrow claims or an unnecessary argument) to preserving maximum value.

With the “having no predefined hierarchical relationship” language in place, the examiner allowed the case and the ‘360 patent issued on August 6, 1996.


Starting in 2009, patent owner SpeedTrack asserted US5444360 against numerous parties, with Amazon being conveniently first-named in the current appeal.  

At the Markman step in 2019 (page 6 of the slip opinion) SpeedTrack advocated “no predefined hierarchical relationships” as a proper claim construction, and the district court adopted that meaning.  SpeedTrack also stipulated (id. at 8) that hierarchical “field-and-value” relationships did not infringe the ‘360 patent.

On appeal, however, SpeedTrack argued that hierarchical descriptions were precluded only among “categories,” but not precluded among “values.”  Id. at 12. The Federal Circuit rejected this, however, on the grounds that (my language) such a construction backed the claims squarely into the Schwartz prior art that necessitated the original “hierarchical” (etc.) amendments.

Thus, the case turned entirely on the issue of the district court’s claim construction.  If the Federal Circuit ruled that the district court’s construction was correct, SpeedTrack would lose.

The Federal Circuit’s opinion briefly reviewed claim construction principles:

  • “Ordinary and customary meaning” and “in view of the specification” (Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005));

  • Clear disavowal of claim scope (Vita Mix v. Basic Holding, Inc., 581 F.3d 1317 (Fed. Cir. 2009));

  • Both amendments and arguments can lead to disclaimer (Tech. Props. Ltd. v. Huawei Techs. Co., 849 F.3d 1349, 1357 (Fed. Cir. 2017); Andersen Corp. v. Fiber Composites, LLC, 474 F.3d 1361, 1374 (Fed. Cir. 2007));

  • De novo review (Teva Pharms. USA, Inc. v. Sandoz, Inc., 574 U.S. 318, 331–32 (2015));

and the big enchilada;

  • The applicant patentee cannot construe claims one way to obtain allowance and a different way to capture alleged infringers (Aylus Networks, Inc. v. Apple Inc., 856 F.3d 1353, 1360 (Fed. Cir. 2017)).

As set forth with respect to the prosecution history, SpeedTrack had clearly disavowed the “hierarchical relationship” between fields and values for those fields.  As a result, the hierarchical methods carried out by the numerous defendants did not infringe and SpeedTrack lost the appeal.

Can SpeedTrack help us identify some factors that patent practitioners should keep in mind?

First with apologies to Jack Webb, “Anything you say can and will be used against you in a court of law.”  Thus, if you don’t need to say it, then don’t say it.

Second, in claims every word matters.  Any word that your competitor can avoid (e.g., “cotton T-shirt” versus “T shirt”) should likewise be avoided.

Third, arguments matter.  Therefore, arguments during prosecution should be closely tailored to the relevant art and should avoid speculation or possibilities that may not matter. 

Note that none of these factors relate to common modern metrics such as which owners (or which law firms) filed the most patents last year, or which examiners are “hardest,” or “how many office actions did you take” or “you filed a lot of (or very few) continuing applications“, or area-of-technology mapping.

No.  For any given patent, good claim drafting and minimizing admissions in the prosecution history provide the client—the inventor or patent owner—with the best value.  This is particularly true for clients for which a fewer number of patents represent the crown jewels.

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