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I would like to ask about the status of a patent if an independent claim is found to have been anticipated by a previous patent but a claim that is dependent on it has not.

For example, what would be the position of a particular US patent if at some point following the issue of the patent, claim 1 is found to be invalid because of the late discovery of an earlier patent covering the subject matter of that claim, but claim 2 which is dependent on claim 1 does not appear to have been anticipated.

Clearly the patent can no longer rely on claim 1, but is it legally enforceable with respect to claim 2? That is, if someone infringes claim 2, can the inventor use claim 2 to protect his or her right to the subject matter in that claim?

Or does claim 2 become invalid on account of the fact that it is dependent on an invalid claim. In that circumstance can the inventor do anything to maintain patent cover with respect to claim 2?

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Each claim in a patent stands on its own. Claim 1 may be invalid but claim 2 may be valid and infringed. In other words, even if independent claim 1 is anticipated, claim 2 may be valid and infringed.

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    Well, yes, but the keyword here is "may". There is no automatic limitation to a dependent claim. The scope of a granted patent is defined by its independent claims. If these are found to be not novel, the patent is invalid. It may be possible to limit the scope to a dependent claim in invalidity proceedings, but this is in no way automatic.
    – Dr. Stephen Falken
    Commented Jan 22, 2015 at 18:03
  • Just checked Patent Law Essentials which states..."The presumption of validity applies separately to each claim of a patent. Even if Claim 1 has been proven invalid by clear and convincing evidence, Claim 2 is unaffected until a challenger proves that it, too, is invalid." This would imply continuing validity to any dependent claim that is not proved to be invalid. Would this mean though that the patentee could continue to use the existing patent (that would from then on not be protective of independent Claim 1) or would he have to redraft the patent with a new list of claims.
    – Michael Ridgway
    Commented Jan 22, 2015 at 20:08

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