It's usually easy to spot a dependent claim. They will immediately go to the first person they know at a party and follow them around for the whole evening. They text too much. They may boil your pet rabbit.
They also usually begin with something like "the compound of claim one, wherein the R1 group is cocktail sauce or raspberry jam"
But what do you make of a claim like this?
A method of performing an assay that monitors cell-substrate impedance, comprising: providing the system of claim 1;
introducing cells into at least one well of said system;
monitoring cell-substrate impedance of said at least one well.
It references a specific system claimed in an an earlier claim (here a fancy sensing wellplate). But it doesn't look at all like the usual form. Instead it pretty much says, "use that well plate we told you about and then look at one happens you big dummy."
(Eds. Note: I should move into prosecution)
The issue came up in the context of a dispute over marking. As shown above, the patent in Agilent Technologies, Inc. v. Axion BioSystems, Inc., C.A. No. 23-198-CJB (D. Del. Jan. 12, 2026) had an independent system claim and these "mixed" method claims that required using the system. It was undisputed that the plaintiff had sold a wellplate that practiced the system claim without marking it.
Years ago, the Federal Circuit held that a party could get around 287 in these circumstances by only asserting the method claims, even if there were other unasserted system claims in the same patent. Crown Packaging Tech., Inc. v. Rexam Beverage Can Co., 559 F.3d 1308, 1316 (Fed. Cir. 2009). But that leaves the question of what to do with a claim like this that actually requires the use of the infringing apparatus?
In granting summary judgement of no pre-suit damages, Judge Burke held that these claims were dependent and thus subject to 287 even if the underlying system claim was not asserted:
In the Court's view, the structure of these asserted claims indicates that pre-suit marking was required, as the claims are each dependent on system claim 1, and (relatedly) facially incorporate the system of claim 1 into the claims. With regard to the dependency issue, in order to establish whether a claim is dependent upon another, the Court examines whether "the new claim both refers to an earlier claim and further limits that referent." The asserted claims here each refer to independent system claim 1, and they each further limit that claim by way of their own additional specific method-related requirements . . . . In light of the above, in order to infringe the asserted claims, a party must make use of the system in claim 1. And so the asserted claims, which include and rely on the use of a system that can be marked, are subject to Section 287(a)'s marking requirement.
Id.
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