An interesting opinion was recently issued by the Federal Circuit concerning how to draft patent claims and the importance of the words used. See Evolusion Concepts, Inc. v. Hoc Events, Inc., No. 2021-1963 (US Fed. Circuit, January 14, 2022).

The case involved a patent related to firearm magazine conversion kits. In particular, the patent at issue — the ‘845 patent — describes a device and method for converting a semi-automatic rifle with a detachable magazine to one with a fixed magazine. A firearm magazine contains bullets. As described by the court, a detachable magazine allows a user to fire the weapon until the magazine is depleted, then release the magazine and insert a new magazine. By contrast, a fixed magazine can not be removed so easily. To replace a fixed magazine, certain non-magazine parts must be disassembled first.

The technical issue involves what are called “magazine catch bars” The ‘845 patented invention replaces the factory-installed standard “original equipment manufacturer” (“OEM”) magazine catch bar assembly. More specifically, the invention in patent ‘845 is described as a “permanent fixture added to a semi-automatic firearm by removing the standard OEM magazine catch assembly and installing the invention.”

The alleged infringer — Juggernaut Tactical, Inc. — began marketing and selling a competing product that also replaced the OEM magazine catch assembly to create a fixed-magazine firearm. The owner of the ‘845 patent — Evolusion Concepts, Inc. — sued claiming patent infringement. Juggernaut argued that it was not infringing the ‘845 patent because its product involved re-use of the original manufacturer’s magazine catch bar assembly, rather than a new or different catch bar.

At the trial level, Juggernaut won on summary judgment and the infringement case was dismissed. The district court concluded that the claims in patent ‘845 excluded re-use of a factory-installed magazine catch bar.

However, on appeal, the Federal Circuit Court of Appeals reversed. The key for reversal was how the patent claims were stated. The ‘845 patent had three independent claims and, in each claim, the phrase “a magazine catch bar” was used. The Court of Appeals found it significant that the claims used the word “a” before the words “magazine catch bar,” instead of antecedent-basis language such as “said” or “the.” As the court explained:

“The inventors, in the independent claims, did not choose to claim a device with the original OEM magazine catch bar, specifically. Rather, they claimed “a magazine catch bar,” which through the use of the indefinite article “a” reads on any magazine catch bar, including the existing OEM component.”

Why Indefinite vs. Definite Articles Change Everything in Patent Law

The distinction between “a,” “the,” and “said” is not grammatical pedantry — it is a fundamental rule of patent claim construction that has been applied consistently by the Federal Circuit for decades. The rule derives from the concept of antecedent basis. In patent drafting, the first time an element is introduced into a claim, it is typically introduced with the indefinite article “a” or “an.” This introduction establishes the element in the claim. Each subsequent reference to that same element must use “the” or “said” to indicate that it is referring to the same, already-introduced element — not a new one. When a drafter uses “a” again after the first introduction, it signals a different, unspecified instance of that element.

In Evolusion Concepts, because the claims used “a magazine catch bar” throughout — including in dependent claims — rather than “the magazine catch bar” or “said magazine catch bar,” the Federal Circuit held that the claim language covered any magazine catch bar, including one already installed on the firearm. This meant Juggernaut’s reuse of the OEM catch bar did not escape infringement because the claim language did not require a new catch bar. The lesson is stark: a single-word choice can determine whether a patent claim covers a competitor’s product.

The Role of Claim Construction in Patent Litigation

Before a district court can decide whether a patent has been infringed, it must first determine what the patent claims actually mean — a process called claim construction. Claim construction is a question of law, not fact, which means it is reviewed de novo (without deference) on appeal. This is why the Federal Circuit was free to reverse the district court’s summary judgment ruling in Evolusion Concepts: the district court’s interpretation of the claim language was legally incorrect, not merely a disputed fact.

The Supreme Court established the foundational framework for claim construction in Markman v. Westview Instruments, Inc., 517 U.S. 370 (1996), holding that claim construction is exclusively a matter for the judge rather than the jury. In many patent cases, a court will hold a “Markman hearing” dedicated solely to construing the disputed claim terms before trial. The outcome of that hearing often determines the outcome of the entire case, because a favorable or unfavorable construction can make infringement impossible to prove or impossible to deny.

Prosecution History and the Doctrine of Prosecution History Estoppel

Claim language does not exist in a vacuum. Courts also examine the patent’s prosecution history — the record of the applicant’s correspondence with the USPTO during examination. If an applicant amended a claim or made an argument to distinguish prior art during prosecution, those actions can narrow the scope of the claim through prosecution history estoppel, even if the plain language of the claim as issued would otherwise be broad. Conversely, statements made during prosecution can sometimes be used to support a broad interpretation if the drafter consistently used open-ended language to cover multiple embodiments.

This interplay between claim language and prosecution history means that patent attorneys must exercise care not only in drafting claims but in every argument and amendment made during examination. A narrowing amendment made to overcome a prior art rejection can surrender claim scope that was never intended to be given up, under the doctrine established in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002).

Practical Drafting Principles for Patent Applicants

The Evolusion Concepts decision reinforces several best practices for patent applicants and their attorneys:

• Use “a” intentionally for broad coverage. If you want a claim element to read on any instance of that element — including one already present in a device — use the indefinite article and do not limit it later with “the” or “said” in the same claim.
• Use “the” or “said” to limit scope to a specific introduced element. If you need to tie a later claim step back to a specific, previously introduced element, use “the” or “said” to establish that the reference is to the same element.
• Maintain consistent antecedent basis throughout. Every use of “the” or “said” must have a clear antecedent — a prior “a” or “an” introduction in the same claim. Lack of antecedent basis can render a claim indefinite and invalid under 35 U.S.C. § 112.
• Draft multiple independent claims with varying scope. Different independent claims can use different language to capture different infringing scenarios. A narrower claim that specifically covers a new element and a broader claim that covers any element — old or new — together provide complementary protection.
• Review claim language in light of known competing products. Before filing, consider how a competitor might try to design around the claims and whether the chosen language leaves gaps that would allow that workaround.

Contact Revision Legal

Patent claim drafting is one of the most technically demanding skills in intellectual property law. The attorneys at Revision Legal draft, prosecute, and litigate patents across a wide range of technologies. If you are developing a new invention or facing a patent infringement dispute, contact us today for a consultation.