Devil in the Details: Does ‘A’ Mean ‘One’ or ‘At Least One’?

“Patent drafters should be cautious about the proper use of the indefinite articles ‘a’ and ‘an.’”

A -“A” is one of the smallest words, but it is not the simplest—most Supreme Court judges can disagree on its meaning. In Niz-Chavez v. Garland, 141 S. Ct. 1474 (2021), the Court issued a 5-3 decision and held that “a” meant “one” in a statute regarding “a notice to appear.” Although the Niz-Chavez case is not about patent claim interpretation, it behooves us to pay attention to this tiny word. Soon after the Supreme Court decision, this issue has appeared again, this time in a patent case.

One or More

In Azurity Pharms., Inc. v. Alkem Lab’ys Ltd, No. CV 19-2100-LPS, 2021 WL 5332406 (D. Del. Nov. 16, 2021), the parties disputed the term “a buffer,” which appears in three related patents. The claim granted by the U.S. Patent and Trademark Office (USPTO) generally follows this format: A formulation, consisting essentially of (i) enalapril or a pharmaceutically acceptable salt or solvate thereof; (ii) a buffer; (iii) a preservative that is sodium citrate; and (iv) water. The issue is whether “a buffer” should mean only one buffer or at least one buffer.

The court highlighted a general principle that the word “a” or “an” means “one or more” unless a patentee clearly intends to limit “a” or “an” to “one” in the specification, the claims, or the prosecution history. The court also noted that this general rule often applies to open-ended claims or partially opened claims characterized by “consisting essentially of.”

The court found this general rule applies to the claim at issue because of its partially opened nature. The court further found that the specification language that “the singular forms ‘a’, ‘an’, and ‘the’ include plural reference unless the context clearly dictates otherwise” further supports this interpretation. Given the conventional rule in light of the specific definition in the specification, the court reasoned that “a buffer” means “one or more.”

The defendant argued that the patentee’s statements in the prosecution history of the parent patent constituted a disclaimer of additional ingredients, including multiple buffers. The defendant alleged that the patentee distinguished the parent patent from the prior arts based on a narrow set of ingredients and recited the patentee’s language that “none of [the prior art]” references teach[es] or suggest[s] the claimed combination of only enalapril, citric acid, sodium citrate, sodium benzoate, sucralose and water at the recited concentrations and pH.” Additionally, in the prosecution of a related patent application, when the patent examiner counterargued that the open-ended nature of the term “comprising” did not explicitly exclude additional components, the patentee amended “comprising” to “consisting essentially of” to overcome the examiner’s argument.

The court disagreed and emphasized that a disavowal must be clear and unequivocal. The patentee merely argued that the claimed invention had only four components to distinguish from the ten or more ingredients in the prior arts. The patentee never took a single buffer as a unique element to distinguish the claim from the multiple buffers contained in the prior arts. The fact that the patentee amended “comprising” to “consisting essentially of” instead of “consisting of” further suggests that the patentee does not disclaim all embodiments having multiple buffers.

Therefore, the whole application and the prosecution history do not evince a clear and unmistakable disclaimer from the conventional rule that “a” means “one or more.” The term “a buffer” should be constructed as “at least one buffer.”

One and Only One

However, indefinite articles “a” or “an” do not always mean “one or more.” In Aug. Tech. Corp. v. Camtek, Ltd., 655 F.3d 1278, 1282 (Fed. Cir. 2011), the claim at issue recites “a wafer provider for providing a wafer to the test plate; a visual inspection device for visual inputting of a plurality of known good quality wafers during training and for visual inspection of other unknow quality wafers during inspection.” The issue was whether “a wafer” is also “a plurality of wafers.” The court held that “a wafer” here should mean “one and only one wafer.” The court reasoned that constructing “a wafer” as “a plurality of wafers” would render “a wafer” superfluous since a claim interpretation that gives life to all the terms is better than one that makes certain terms redundant. The court also looked into other patents of the same family and found that if “a wafer” were a plurality of wafers, the art would not work. Moreover, the specification consistently takes wafers as discrete items. Considering the claim language in light of the specification, the court concluded that “a wafer” means “one and only one wafer.”


Patent drafters should be cautious about the proper use of indefinite articles “a” and “an.” Generally, when a claim is open-ended or partially open-ended, the term “a” or “an” means “one or more” unless the context indicates otherwise. However, this is not a hard and fast rule, and the indefinite articles “a” or “an” can mean “one and only one.” Patent drafters should ensure consistency between statements in the prosecution and the application. Since the same term in related patents presumably have the same meaning unless otherwise compelled, practitioners should properly manage a patent family as a whole and ensure consistency among different patents.

It is also essential to properly use plural forms to avoid ambiguities in words that have two acceptable plural forms. For example, in the August case, a whole wafer was typically diced into many pieces, called “dies.” In fact, “die” is an acceptable plural form of “die”, but the patentee used “dies” to avoid it being interpreted in the singular.


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Join the Discussion

12 comments so far.

  • [Avatar for concerned]
    June 22, 2022 12:47 pm

    THE Ohio State University now has a trademark on “THE.”

    THE Ohio State University also is one of two university studies submitted on my record as evidence to support my patent application.

    The, not THE, USPTO ignored my evidence but did not ignore THE Ohio State University trademark.

    Maybe I should resubmit THE evidence?

    Crypto and USPTO both end with P-T-O. Interesting don’t you find?

  • [Avatar for Anon]
    June 16, 2022 10:43 am

    Mr. Bertini,

    Do you have a link? I would be interested in understanding the context of the case (as a judge cancelling the registration may – and critically, may not – have anything to do with the point at hand of “Does ‘A’ Mean ‘One’ or “At Least One’?)

  • [Avatar for James Bertini]
    James Bertini
    June 15, 2022 03:38 pm

    In a case to cancel URBAN HOMESTEADING on the supplemental register, the TTAB decided on March 31, 2014 that the words of section 1092 of the Lanham Act which require “a hearing” don’t mean a single hearing, but rather unlimited hearings (“an opportunity to be heard judicially in a cancellation proceeding”).

    This defeats the entire purpose of section 1092 which sets up the equivalent of a small claims procedure to cancel a supplemental registration whose owner has abused it by asserting rights of a principal registration.

    The Board achieved this clever decision by discussing the word “hearing” in the statute, pretending that the article “a” didn’t precede it.

    One of the petitioners then took the case to federal court, where the judge didn’t brook any nonsense and cancelled the registration.

  • [Avatar for C. Whewell]
    C. Whewell
    June 14, 2022 02:12 pm

    But….. ya’all….. what is “a buffer”, other than being a “means for…..” ?

    It is a means-for controlling pH.

    So, 112(f) maybe should kick in…..

  • [Avatar for Joachim Martillo]
    Joachim Martillo
    June 13, 2022 10:43 am

    I probably should not comment in the throws of Covid vaccination reaction.

    Some days I really wish we could write a patent in (classical) Latin, which has no indefinite article. The word unus, -a, -um really means one (exactly). This particularly silly issue of the English indefinite article probably does not arise at a patent office, which operates in a language that has no indefinite article.

  • [Avatar for Anon]
    June 13, 2022 09:42 am

    Pro Say,

    Your pro se nature is NOT helpful here – and whether or not the legal implications of ANY term of language matches your colloquial expectations (or other items that I — with all hope of being helpful – point out to you) – are AS simple as they need to be.

    Remember the second half of Mr. Einstein’s quote (my emphasis added):

    Everything should be made as simple as possible, but not simpler.

  • [Avatar for concerned]
    June 13, 2022 08:56 am

    Josh Malone’s comments about legal ingenuity hits home with me.

    Asst. Solicitor using collateral estoppel as an argument with cases that are cherry picked and did not have the same level of evidence (evidence from every possible end user), engrafting words on to the written law and refusing to define said words, and giving rejection theories that are inconsistent with the official record all seem to be legal ingenuity to prevent me from getting a patent.

    Arguing routine, well understood and conventional when nobody has ever used any of my components, individually or in combination, seems to be legal ingenuity.

    Arguing mental steps when I think nobody can do my process in their mind on just 10 people, let alone 1.5 million people in my State, is legal ingenuity. I have a standing challenge if someone wants to prove mental steps.

    Whether “A” is “A” does not surprise me. Suggestion: Add “A” to USPTO: United States (Anti) Patent and Trademark Office.

  • [Avatar for Joachim Martillo]
    Joachim Martillo
    June 12, 2022 11:11 am

    Some days I really wish we could write a patent in (classical) Latin, which has no indefinite article. The word unus, -a, -um really means one. This particularly silly issue does probably does not arise at a patent office, which does not operate in a language that has no indefinite article.

  • [Avatar for Pro Say]
    Pro Say
    June 12, 2022 10:11 am

    My good friend Anon. Please stop trying to make that which is simple and obvious . . . complicated. You’re better than this.

    One is one is one. A is A is A.

    Legally. Factually.

    Had SCOTUS wanted multiple abstract allegations against the same claim/s to be acceptable, they would have said so.

    But. They. Did. Not.

  • [Avatar for Anon]
    June 12, 2022 08:41 am

    Pro Say,

    Please stop with your incorrect view of the Supreme Court decision in regards to “ even though SCOTUS in Alice repeatedly said to identify A / ONE abstract idea.

    From a legal standpoint, you simple have no basis for your view.

    I have explained this previously, and you are falling into the category of expounding an opinion that is WORSE than being merely uninformed.

    Instead of advancing your cause (whatever that may be), you diminish any persuasion that you may otherwise have.

  • [Avatar for Pro Say]
    Pro Say
    June 11, 2022 05:03 pm

    Does ‘A’ mean one, or at least one?

    Silly question.

    In far too many cases, ‘A’ means whatever it has to in order to take away an invention from an inventor or patent owner . . . and give it to the infringer.

    The most sickening, despicable example of this . . . is the CAFC post-Alice permitting multiple (supposed) abstract ideas to be asserted against a claim . . . even though SCOTUS in Alice repeatedly said to identify A / ONE abstract idea.

    Here in America, patent invalidation / prevention reigns supreme.

  • [Avatar for Josh Malone]
    Josh Malone
    June 11, 2022 01:28 pm

    The courts should consider whether the accused infringer is practicing the essence of the invention. Legal ingenuity should not be more profitable than technological ingenuity. Adding a routine 2nd buffer while relying on the teaching of the inventor of the first buffer to solve the problem isn’t fair.