In Baldwin Graphic Systems, Inc. v. Siebert, Inc., the Federal Circuit confirmed that the use of the indefinite articles "a" or "an", in an open-ended claim containing the transitional phrase "comprising", carries the meaning of "one or more".
Baldwin sued Siebert for infringement of a number of claims in its patents of systems for cleaning a cylinder of a printing press using cleaning fabric and methods for making those systems. The District Court found no infringement, construing the phrase "a pre-soaked fabric roll" to mean a single roll and relying on the subsequent use of the phrase "said fabric roll" to reach that conclusion. The Federal Circuit disagreed, stating that “[t]his court has repeatedly emphasized that an indefinite article ‘a’ or ‘an’ in patent parlance carries the meaning of ‘one or more’ in open-ended claims containing the transitional phrase ‘comprising'" and emphasized that such an interpretation is best described as a rule, rather than a presumption or convention.
Additionally, the Federal Circuit stated that the subsequent use of the term "said" or the definite article "the" does not change the plural rule, but rather simply reinvokes the non-singular meaning. Exceptions to the rule arise only where a patentee "evince[s] a clear intent to limit 'a' or 'an' to 'one'" or where the language of the claims themselves, the specification, or the prosecution history necessitate a departure from the rule.
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