Originally published in Law360, New York on August 13, 2012.

Patents are presumptively valid under 35 U.S.C. § 282 and can be proven invalid only by clear and convincing evidence. Thus, accused infringers hoping to prove a patent invalid must do so by satisfying a heavy burden. This is partly based on “the basic proposition that a government agency such as the then Patent Office [is] presumed to do its job.” But critics complain that such great deference to the Patent Office makes little sense when measuring a patent against prior art that the Patent Office didn’t know about — or, as in Sciele Pharma Inc. v. Lupin Ltd., when the Patent Office issued a patent with errors.

In Sciele, the Federal Circuit confirmed that the burden of proof does not depend on whether the Patent Office considered the prior art being offered against the patent during litigation — or even on whether the Patent Office made an obvious mistake when it granted the patent in suit. According to the court, facts like those go to the weight of the evidence at hand, not to the total weight of evidence required to invalidate a patent. In the Sciele court’s words...

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