To Specify a Further Limitation.
In the recent case of Pfizer, Inc., et al. v. Ranbaxy Laboratories, Limited, et al., a claim was found invalid for being improperly dependent in form. Pfizer had apparently stipulated at District Court that the claim at issue was a dependant claim and not an independent claim, thus (in hindsight) leaving itself open to the holding in this opinion. The claim at issue did reference another claim, but was drawn to different subject matter (a hemicalcium salt instead of a compound of claim 1). I believe this case does prompt the interesting question, therefore, of what actually differentiates an “independent” claim from a “dependent” claim under U.S. patent law?
Conveniently, dependent claims are defined at 35 U.S.C. Section 112, paragraph 4, which states:
“[A] claim in dependent form shall contain a reference to a claim previously set forth and then specify a further limitation of the subject matter claimed. A claim in dependent form shall be construed to incorporate by reference all the limitations of the claim to which it refers.”
Thus, a dependent claim has two elements: (1) the claim must contain reference to a previous claim, and (2) the claim must specify a further limitation to the previous claim.
The first of these elements is easily recognized . . . just a mere reference to another claim will suffice. But what does it mean to “specify a further limitation?” Does almost any reference coupled with additional subject matter act as a limitation, or can a claim actually reference another claim without providing a further limitation? For example, does a claim that states “An article prepared according to the process of Claim 1” act to further limit the process of claim 1 by reciting a particular article made by the process, or does it instead recite independent subject matter, i.e. an article and not a process, and thus should be considered an independent claim?
I am of the view that almost any reference (there may be a few exceptions) to another claim results in the claim becoming dependent in form, regardless of whether the new claim is drawn to different subject matter. I see language drawn to different subject matter, but presented in such as fashion, as a further limitation of the independent claim. I believe the better practice is to write such claims in truly independent form, especially if it is the intent that the claims be viewed as such.
I know of some colleagues who disagree with this viewpoint, and feel that referencing another claim but reciting different subject matter makes the claim independent, in particular because they do not view the recitation of different subject matter as a limitation. Any other practitioners out there feel strongly about this topic one way or another? Thoughtful comments are welcomed.