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I'm following an Inter Partes Review where the petitioner is trying to invalidate every independent claim of a patent based on prior art.

If this is successful, some dependent claims will remain. Some are as simple as "the system of claim 1 where the {thing} calls a script". "the system of claim 1 where the {thing} is incorporated into a web browser".

It's my understanding that each claim is considered alone so the 'web browser' claim still stands even if its independent parent is invalid.

Given that using a web browser is almost essential it therefore seems like the patent owner is left with an enforceable patent by adding the words 'in a web browser' to prior art.

If EvilCorp decided to sue based on its surviving dependent claim how would infringement likely be evaluated? Would a court disregard the bulk of the invalid claim and only consider whether the addition of a web browser or the use of a script is sufficiently non-obvious?

In other words, is trying to sue based on a dependent claim from an invalid independent claim a much weaker legal position?

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For an infringement claim to hold, it must pass the all-element rule. For example,

  • Claim #1 contains element A, B, and C
  • Claim #2 contains element D
  • Claim #2 is dependent on #1

Infringement on claim #2 is not possible unless the alleged infringing device contains A, B, C, and D.

However, if the dependent claims aren't particularly novel, and then they are probably susceptible to invalidation as well.

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  • I like this answer. But it does jump from the term "invalidity" in the original post, to "infringement" in the answer. This is ok, however because, “That which infringes if later, anticipates if earlier.” Peters v. Active Mfg., 21 F. 319 (W.D.Ohio 1884) (affirmed and quoted in 129 U.S. 530 (1889)) (as quoted on Patently-o).
    – user16642
    May 5, 2016 at 18:10
  • @user16642, daniel makes that jump because that is the entirety of the correct answer: the invalidity of the independent claim did not in effect delete the independent claim from the patent. Instead the invalidity in effect swept the independent claim into the dependent claim to transform the dependent claim into a de-facto independent claim via all the overt & implied logical-ANDs accumulating.
    – Andreas ZUERCHER
    Apr 6, 2022 at 13:55

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