Construction of “A”.
In a rule of construction somewhat in conflict with normal usage of the terms, the Federal Circuit has generally construed the terms “a” and “an” to mean“one or more” in open-ended claims containing the transitional phrase “comprising.” See, e.g., KCJ Corp. v. Kinetic Concepts, Inc. (Fed. Cir. 2000, 99-1248). Unless the claim is specific as to the number of elements, the term “a” receives a singular interpretation only in rare circumstances when the patentee evinces a clear intent to so limit the term. Accordingly, barring the rare circumstances described below, a claim reciting “an element” will likely be interpreted by courts to recite “one or more elements.”
This general rule does not apply when the specification or the prosecution history shows that the term was used in its singular sense. See, e.g., Elkay Mfg. Co. v. Ebco Mfg. Co. (Fed. Cir. 1999, 98-1596, 99-1276). Thus, if the specification does not support the possiblity of more than one of the elements recited in conjunction with the terms “a” or “an”, then a the claim will be construed more narrowly to include only the singular element.
Another reason, particularly in light of Phillips v. AWH (previous AT! analysis), why practitioners should take care to write a solid specification in addition to a solid set of claims.