Reinvigorated Enforcement of Evidentiary Rules and the Permissible Uses of General Knowledge in Inter Partes Review

On July 31, 2025, the Acting Director of the US Patent and Trademark Office (USPTO) issued a significant memorandum that alters the evidentiary landscape for inter partes review (IPR) proceedings before the Patent Trial and Appeal Board (PTAB). The new guidance, which applies to all IPR petitions filed on or after September 1, 2025, ends the agency’s discretionary waiver of the evidentiary rule found in 37 C.F.R. § 42.104(b)(4). As a result, petitioners will be prohibited from using non-publication evidence to supply a claim limitation that is missing from the asserted prior art patents and printed publications. The memo, “Enforcement and Non-Waiver of 37 C.F.R. § 42.104(b)(4) and Permissible Uses of General Knowledge in Inter Partes Reviews,” supersedes two prior memos on the topic from August 2020 and June 2022 that had permitted a more flexible approach.

Key Takeaways

• Strict Enforcement of an Existing Rule: The memo does not create a new rule, but rather ends the USPTO’s discretionary waiver of the rule that IPRs be based only on patents and printed publications. This reverses the more permissive stance taken in the 2020 and 2022 guidance memos.
• “Missing Elements” Cannot be Filled by Testimony or Common Sense: The memo explicitly states: “Applicant admitted prior art (AAPA), expert testimony, common sense, and other evidence that is not ‘prior art consisting of patents or printed publications’ may not be used to supply a missing claim limitation.”
• Permissible Uses of General Knowledge: This “general knowledge” evidence may still be used for other purposes, such as providing context, demonstrating the knowledge of a person of ordinary skill in the art (POSITA), or supplying a motivation to combine prior art references that, together, disclose all claim limitations.
• Aligning with Federal Circuit Precedent: The memo states the change is being made because the prior guidance is “no longer consistent with Federal Circuit precedent,” including the decisions in Qualcomm v. Apple and Shockwave v. Cardiovascular Systems.
• Advantage for Patent Owners: This change provides patent owners with a powerful new defense. They can now more readily defeat an IPR petition at institution by showing that the petitioner has impermissibly relied on an expert’s declaration or an alleged “common sense” argument to patch holes in the cited references.

Enforcement of Existing Rules

The memo’s change is a shift in enforcement policy. The statutory basis for IPRs, 35 U.S.C. § 311(b), limits invalidity grounds to prior art “consisting of patents or printed publications.” The corresponding regulation, 37 C.F.R. § 42.104(b)(4), requires a petition to “specify where each element of the claim is found in the prior art patents or printed publications relied upon.” The USPTO’s 2020 and 2022 memos had effectively waived strict enforcement of this rule, allowing petitioners to use AAPA to supply missing limitations.

This practice was rendered inconsistent with the law by the Federal Circuit. In Qualcomm Inc. v. Apple Inc., the court held that AAPA could not form the “basis” of an IPR challenge. While the subsequent decision in Shockwave Medical, Inc. v. Cardiovascular Systems, Inc. suggested a narrow path might exist to use AAPA as “background knowledge” to supply a limitation, the Director’s new memo forecloses this interpretation for practitioners.

The memo clarifies the crucial distinction between two uses of evidence:

1. Impermissible Use (Supplying a Missing Limitation): A petitioner cannot argue that a primary reference discloses elements A and B, and that element C was simply within the general knowledge of a POSITA. The petitioner must point to a patent or publication that discloses C.
2. Permissible Use (Motivation to Combine/Context): A petitioner can cite Reference 1 for elements A and B, and Reference 2 for element C. The petitioner may then use expert testimony or other evidence of “general knowledge” to explain why a person of ordinary skill in the art would have been motivated to combine Reference 1 and Reference 2.

Strategic Considerations for Practitioners

For Petitioners:

• Thorough Prior Art Searching is Paramount: The inability to fill gaps with testimony means that the initial prior art search is more critical. Petitioners must locate references that explicitly or inherently disclose every limitation.
• Petition Drafting: Petitions must be drafted precisely, creating a clear and direct map from each claim element to a specific location in a cited patent or publication. Any ambiguity will be a target for the patent owner.

For Patent Owners:

• Scrutinize Petitions for Gaps: Patent Owner Preliminary Responses, or Discretionary Denial Briefs, should now include a focused analysis of whether the petition improperly uses general knowledge to supply a missing element, rather than just for context or motivation.
• Strengthened Patents: This guidance arguably strengthens the presumption of validity for patents with claim limitations that were not explicitly captured in patents or printed publications.