TAKEAWAY: The Federal Circuit confirmed the general rule that the articles “a” and “an” in patent claims are presumed to mean “one or more,” absent sufficient context providing otherwise.

In its opinion ABS Global Inc. v. Cytonome/ST, LLC dated October 19, 2023, the Court of Appeals for the Federal Circuit in reconfirmed the general rule that articles “a” and “an” in patent claims should be construed to mean “one or more.”

ABS petitioned for inter partes review in the USPTO of Cytonome’s US Patent No. 10,583,489, relating to a microfluidic device. ABS argued that the claims were invalid as anticipated by and/or obviousness over prior art references. In its final written decision, the Patent Trial and Appeal Board construed the term “a sample stream” in the challenged claims to require a single stream only and to exclude a plurality of streams. On this basis, the Board found that the prior art references failed to disclose the single stream and therefore upheld validity of the claims.

On appeal, the Federal Circuit rejected the Board’s claim construction and concluded that the claims were not limited to a single stream only. First, the Court noted that claims using open-ended “comprising” language, like the claims at issue, “a” or “an” followed by an object requires “one or more” of the object “unless the context sufficiently indicates otherwise.” The Court found that neither the patent specification nor the prosecution history provided any “clear and manifest disavowal” of the general rule, noting that the specification indeed specified that “a” or “an” referred to “one or more.” Moreover, the Court found that no “operational impossibility” required rejection of a plural meaning. The Federal Circuit reversed in part, vacated in part, and remanded the case to the Board.

While this case reconfirms a general rule, patent drafters would be well served to include an explicit statement in the specification when they intend “a”/”an” to be interpreted as “one or more”. Drafters should also be mindful of statements included in the specification or made during prosecution that could be construed as disavowing or otherwise contradicting a plural meaning. If in doubt, replacing “a”/”an” articles in claims with “one or more” remains an option, albeit a less elegant option, to make clear that claims are not limited to singular-only variations.