Claim Indefiniteness Under 35 USC 112

On May 4, 2026, in Enviro Tech Chemical Services, Inc., V. Safe Foods Corp., the Court of Appeals for the Federal Circuit invalidated a set of patent claims that contained the word “about” as being indefinite under 35 USC 112. The court noted that there appropriate uses for words like “about” and “approximately”, but that this was not the case here.

As originally filed, the claim that became patent claim 1 recited “a pH of about 6 to about 9”. After extensive prosecution, the claim was eventually amended to “a pH of about 7.6 to about 10” to avoid prior art which had a pH of 7.0.

The court noted that the specification did not provide any guidance as to the scope of the term “about” with reasonable certainty. For example, at least one time, it attached significance to differences of 0.3 pH, whereas at other times it mentioned the significance of deviations between 0.35 and 0.5 pH. Therefore, the court concluded that 0.3 was not “a firm indicator of the meaning of ‘about’”.

The court was also troubled by the fact that during the prosecution, the Applicant was inconsistent in its use of “about”. Specifically, the court stated:

We then turn to the '321 patent's prosecution history. Enviro Tech's treatment of the word "about" during the patent's prosecution was inconsistent and also fails to inform a skilled artisan of claim 1's scope with reasonable certainty. For example, in one office action response, Enviro Tech argued that "a peracetic acid solution at the lower end of the claimed range, pH 7.6," would not have been obvious over the prior art, notably failing to include the term "about" in its arguments. J.A. 658. Yet on the next page of its response, with respect to another claim, Enviro Tech argued that "a step of adjusting the pH to the range of about 8 to about 9" would not have been obvious over the same prior art, including "about" in its arguments. J.A. 659 (emphases added).

The court cited Infinity Comput. Prods., Inc. v. Oki Data Ams., Inc., 987 F.3d 1053, 1059 (Fed. Cir. 2021) stating that "Indefiniteness may result from inconsistent prosecution history statements where the claim language and specification on their own leave an uncertainty that, if unresolved, would produce indefiniteness."

For the foregoing reasons, the Court held that the claims were indefinite under 35 USC 112, and thus invalid.

Practice Tips

First of all, claim terms like “about” are quite commonly used. Sometimes Examiners object to them, but frequently, they are accepted. However, it is important to keep in mind that such terms may carry risks that are not necessarily avoided simply because they survived prosecution.

As stated by the court, words like “about” and “approximately” may be appropriately used to “avoid[] a strict numerical boundary to the specified parameter.” As these words are sometimes allowed, it can be particularly tempting to use them when amending to avoid prior art, in view of the potential inapplicability of the doctrine of equivalents to such limitations under the Festo Doctrine. However, the ability to use such language may depend on support in the specification to provide some guidance as to the intended claim scope. And although it may be difficult in some circumstances to provide a precise definition of the intended range or scope of a claim element, it may help to provide goals to be met by the claim.

When using the term “about” or a similar term in a claim that recites a specific numerical value, as a precaution, consider adding a parallel claim that is otherwise the same but does not use the term.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.