Punctuation Pitfalls: Commas and Periods Kill Patents
Thursday, July 22, 2021

A recent article, “The commas that cost companies millions”, highlighted the importance of using proper punctuation in contracts and laws. The article provided examples of punctuation mishaps throughout history, including a $5 million payment for overtime pay to employees due to a missing comma in a statute, and on the flip side, an 1872 American tariff law with an unwanted comma, which cost taxpayers nearly $2 million.

The misuse of punctuation often affects clarity in writing and can have significant consequences. This is especially true with the drafting of U.S. patent applications, where the improper use of punctuation can be destructive to patent owners during litigation.

Several Federal Circuit cases address misplaced punctuation, demonstrating that careless editing and misuse of punctuation can destroy U.S. patent claims. Cases discussed below provide examples of ways, in which punctuation errors can harm patent owners. This blog post highlights the importance of avoiding errors and using proper punctuation when drafting or translating U.S. patent applications.

The Case of the Killer Comma

In Cultor Corp. v. A.E. Staley, 224 F.3d 1328 (Fed. Cir. 2000), the district court and Federal Circuit construed a claim narrowly based on an infelicitous comma. This case involved a process for the commercial manufacture of edible polydextrose, which does not contain bitter-tasting residual compounds. An issue was whether the claims were deemed limited to the specification’s definition of polydextrose prepared using a citric acid catalyst, or based on the interpretations of the claims alone, citric acid and phosphoric acid could be used interchangeably.

The patents at issue in this suit were U.S. Patents Nos. 5,667,593 (“the ’593 patent) and 5,645,647 (“the ’647 patent”). Both the ’593 patent and the ’647 patent are entitled “Modified Polydextrose and Process Therefor,” and are directed to “an improved, water-soluble polydextrose containing 0.3 mol % or less of bound citric acid, a process therefor, and foods containing same.” Cultor Corp, 224 F.3d at 1329. Commercial processing of polydextrose is carried out by the Rennhard process, which includes the step of heating dextrose in the presence of a catalytic amount of citric acid, producing a bitter taste if not removed. Id.

Claims 24, 32, and 33 of the ’593 patent are as follows:

24. A polydextrose composition substantially free of bitter-tasting residual compounds made by the process consisting essentially of:
a) dissolving polydextrose in water;
b) passing said solution through an ion-exchange column; and
c) collecting and concentrating the eluate produced thereby until a commercially useful polydextrose composition is recovered.

32. A polydextrose bulking agent useful for incorporation in reduced-calorie foods, substantially free of bitter-tasting compounds.

33. The polydextrose composition according to claim 32 wherein said bitter-tasting compounds are acidic.

Claim 24 of the ’647 patent as follows:

24. A method for the purification of polydextrose consisting essentially of:
a) dissolving polydextrose in water;
b) passing said solution through an ion exchange column; and
c) collecting and concentrating the eluate produced thereby until a substantially functional product is recovered.

Note that none of these claims recited catalytic citric acid. So, one would think citric acid was not required, and the claim could be open to catalytic phosphoric acid. Wrong! 

According to the specification of both patents, the bitter taste in polydextrose is attributed to the use of citric acid in the Rennhard process, and that some of the citric acid remains bound to the product. Cultor Corp, 224 F.3d at 1330. The ion-exchange procedure removes this bound acid. Id.

In this case, the defendant, A.E. Staley Manufacturing Company (“Staley”), also processed polydextrose by heating in the presence of an acid catalyst and then passed the final product through an ion-exchange resin. However, unlike the ’593 and ’647 patents, Staley used a phosphoric acid catalyst instead of a citric acid catalyst.

Cultor filed suit, alleging infringement.

As noted above, not in the claims, but in the specification, Cultor detailed that the process entails heating dextrose in the presence of a catalytic amount of acid. The specification stated:

As used herein, the expression “water-soluble polydextrose” (also known as polyglucose or poly-D-glucose) specifically refers to the water-soluble polydextrose prepared by melting and heating dextrose (also known as glucose or D-glucose), preferably with about 5-15% by weight of sorbitol present, in the presence of a catalytic amount (about 0.5 to 3.0 mol %) of citric acid.  

See the ’593 patent at 1:24-30 (emphasis added).

The comma after the phrase “preferably with about 5-15% by weight of sorbitol present,” was the culprit. Without that comma, the whole phrase “preferably with about 5-15% by weight of sorbitol present in the presence of a catalytic amount (about 0.5 to 3.0 mol %) of citric acid” would have been optional.

The district court, no doubt having gone to the Tom Irving school of English grammar, ruled that this definition in the specification limited the claims to polydextrose produced with citric acid as a catalyst. Id.

Based on this definition, the district court concluded that Staley, with its use of catalytic phosphoric acid, did not literally infringe. Id. at 1331. The district court also concluded that Staley did not infringe under the doctrine of equivalents, because otherwise the claims “would ensnare the prior art.” Id. at 1330. Ouch! So, the patent owner lost on both literal infringement and doctrine of equivalents infringement.

The district court also highlighted that in the prosecution histories of the ’593 and ’647 patents, the inventors repeatedly distinguished their invention from the prior art by emphasizing their discovery that citric acid caused the bitterness in polydextrose. Id. The inventors emphasized that bitterness could be removed by removing the residual citric acid by means of an ion-exchange resin. Id. The evidence from the prosecution history may not have been necessary but certainly reinforced the effect of the misplaced comma.

On appeal, the Federal Circuit held that the district court did not err in reading the definition of “water-soluble polydextrose” from the specification into the claims. Specifically, the Federal Circuit stated that Cultor explicitly defined this term as limited to a preparation using a citric acid catalyst and disclaimed the other acids. Accordingly, the Federal Circuit held the claims could not be construed to cover what the definition expressly disclaimed, i.e., a phosphoric acid catalyst. The Federal Circuit also affirmed the district court’s finding of non-infringement under the doctrine of equivalents, finding that the doctrine of equivalents was not available to enlarge the scope of the claims to cover other acids.

Besides the fatal comma in Cultor, another punction mark, i.e., the period, left a claim indefinite. In Allen Eng’g Corp. v. Bartell Indus., 299 F.3d 1336 (Fed. Cir. 2002), the Federal Circuit found a claim indefinite under 35 U.S.C. § 112 due to a truncated limitation. Claim 23 of U.S. Patent No. 5,108,220 read:

23. The riding trowel as defined in claim 22 wherein said tertiary linkage means comprises crank means driven by said connecting shaft means and coupled to said gearbox means by rigid

The claim did not contain any punctuation at all at the end of the limitation. The Federal Circuit held that the claim failed to meet the definiteness requirement because it was impossible to discern the scope of the truncated limitation. Note that it was the alleged infringer who figured this out, and not the patent drafter, prosecutor, PTO Examiner, or even, the law firm that brought suit. 


As the cases above demonstrate, the use of proper punctuation is important to ensure claims are interpreted properly during litigation and not invalidated or limited in scope. Accurate punctuation is needed when drafting U.S. patent applications and may be especially difficult when patent applications are translated into English. This problem may be compounded if the translator and/or subsequent drafter does not fully understand the originally chosen language or the intent of the original patent drafter. Although the punctuation may be grammatically correct, as in Cultor, the punctuation may not adequately express the scope of the patent application contemplated, and in Cultor, the comma killed the patent owner’s case of infringement. Drafters need to be aware of the ramifications flowing from English grammar rules. In the case of a translated patent application, it can be difficult to ensure that the intended scope of the claims is maintained in the translation, complicated by the fact that the original patent application was written in a language other than English and may have a different grammatical construct when it comes to commas. 

Stopping a claim in the middle of the phrase, as done in Allen Engineering, can be a critical error leading to indefiniteness. Therefore, in an effort to secure strong, valid, and enforceable claims, drafters should review the claims prior to issuance for not only punctuation but also to catch any inconsistencies or dangling phrases. While technological advances may help identify some of those issues, a final review may be needed to find those grammatical mistakes or typographical errors to avoid any fatalities.

Candace Walther, a Summer Associate, and Stacy Lewis, a Law Clerk, also contributed to this article. 


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