Every court agrees that litigants must support their privilege claims with something other than naked assertions. But they disagree about the type of support required to justify withholding documents or testimony.

In Jeddo Coal Co. v. Rio Tinto Procurement (Sing.) PTD Ltd., the court dropped to a footnote its off-handed assurance that "Rio Tinto may also provide a cover letter or other document that explains the basis for the privilege and identifies the persons who are party to the communications." Civ. No. 3: 16-CV-621, 2018 U.S. Dist. LEXIS 57803, at *20 n.2 (M.D. Pa. Apr. 5, 2018). Most courts require far more. A couple weeks later, in Motorola Solutions, Inc. v. Hytera Communications Corp., the court blasted defendant's privilege claim for one withheld email, sarcastically noting that Motorola's "lawyers assure us, with absolutely no evidentiary support – that the email was the necessary first step in … obtaining legal advice." No. 17 C 1973, 2018 U.S. Dist. LEXIS 64095, at *5 (N.D. Ill. Apr. 17, 2018). The court quoted an earlier Seventh Circuit case for the proposition that "[l]awyers' talk is no substitute for data" – and then pointedly remarked that "[l]ittle wonder that the courts are unanimous in requiring proof of assertions made in briefs." Id. (citation omitted).

Courts' differing attitudes toward the required level of evidentiary support highlight the need for corporations and their lawyers to carefully check the pertinent court's and even the presiding judge's earlier rulings and inclinations.