Terms and Concepts

Standard of Review

The standard of review for patent validity is different in district court litigation than it is before the CRU in patent reexamination proceedings.  In district court, patent claims enjoy a presumption of validity, which may be overcome only by clear and convincing evidence.  In contrast, no such evidentiary presumption exists during reexamination before the PTO.  The PTO and the CRU use a “preponderance of the evidence” standard for adjudicating patentability as MPEP § 706.I. states:  “The standard to be applied in all cases is the ‘preponderance of the evidence’ test.  In other words, an examiner should reject a claim if, in view of the prior art and evidence of record, it is more likely than not that the claim is unpatentable.”

For this reason, challenging a patent’s validity should be easier before the PTO than in the district court.  The district courts determine “validity,” while the PTO reexamines “patentability.”  These terms are used interchangeably, but they are technically different.  Nevertheless, a patent owner faces many practical limitations in its ability to amend claims during reexamination.

No proposed amended or new claim enlarging the scope of claims of a patent is permitted in a reexamination proceeding [35 U.S.C. § 305].  The test for when an amended or new claim enlarges the scope of an original claim is the same as that under the two-year limitation for reissue applications that add enlarging claims under 35 U.S.C. § 251.

After expiration of a patent undergoing reexamination, no amendments may be proposed for entry [37 CFR § 1.121(j)].  Further, any amendments and claims added during the proceeding are withdrawn if a patent expires during pendency of a reexamination proceeding [MPEP § 2250].  As noted herein, if claims are amended substantively, liability for past damages is put at serious risk.


  • Clear and Convincing Evidence
  • Preponderance of the Evidence [MPEP § 706.I]