Claims of a patent define the scope of protection. The elements of a claim are sometimes referred to as limitations, since they limit the scope of protection by requiring the infringed item to have certain features. While most claims positively recite the required elements, it is also possible for claims to exclude certain features - meaning that the allegedly infringing item must not have them. These are referred to as negative claim limitations. Previous posts have discussed issues related to negative claim limitations here and here.
Examiners at the USPTO often ignore negative claim elements on the theory that if a cited reference simply doesn't mention the negative feature, it therefore discloses that feature. Further, Examiners will go so far as to assert, without authority, that negative claim limitations per se do not further limit the claim and therefore can be ignored altogether.
This can be frustrating because case law and the MPEP make clear there is no problem with negative claim elements, and that they do limit claim scope. MPEP 2173.05 states that "there is nothing inherently ambiguous or uncertain about a negative limitation." However, more to the point, the recent Federal Circuit case of Santarus, Inc. v. Par Pharm., Inc. 694F.3d1344, (Fed. Cir. 2012). The claim at issue was directed to a method for treating gastric disorders. The claim specified a treatment method where the “composition contains no sucralfate.” The court stated that the “claim limitation specifying that sucralfate is not administered in conjunction with the Phillips formulation restricted the claims to this preferred use of the Phillips formulations. This exclusion narrowed the claims, as the patentee is entitled to do.” (emphasis added). The idea that negative claim limitations are non-limiting, as a general rule, is a rather silly proposition.
However, the Federal Circuit's Santarus decision is highly applicable to the prosecution context, as the Court cites previous case law confirming that “[n]egative limitations to claims may arise in a variety of circumstances. For example, a negative limitation may be prudently placed in a claim in response to an examiner’s rejection, perhaps to distinguish a reference that was given its “broadest reasonable interpretation” for purposes of examination. See, e.g., In re Skvorecz, 580 F.3d 1262, 1268 (Fed. Cir. 2009).” For another example confirming that an exclusion of claimed elements narrows the claims, see in re Johnson 558 f.2d 1008, 1019 CCPA 1977 (where applicant narrowed the claim to exclude a lost interference count.)
So, the next time you are faced with an Examiner refusing to give patentable weight to a negative claim element, it may be helpful to point out controlling case law to support your arguments.