For more than a decade, United States District Courts have taken a stark approach to the need for appropriate class definitions and ascertainability in federal class actions. Mueller v. CBS, Inc., 200 F.R.D. 227, 233 (W.D. Pa. 2001) (a class definition cannot be “amorphous, vague or indeterminate.”); Adair v. Johnston, 221 F.R.D. 573, 577 (M.D. Ala. 2004) (“[F]or a party to represent a class, the class sought to be represented must be adequately defined and clearly ascertainable.”).

The United States Courts of Appeals have followed suit. Young v. Nationwide Mut. Ins. Co., 693 F.3d 532, 538 (6th Cir. 2012) (“There can be no class action if the proposed class is amorphous or imprecise.”); Brecher v. Republic of Argentina, 806 F.3d 22, 26 (2d Cir. 2015) (“The lack of a defined class period . . . makes the modified class insufficiently defined as a matter of law.”); Mullins v. Direct Digital, LLC, 795 F.3d 654, 659-60 (7th Cir. 2015) (collecting cases).

On November 23, 2020, the United States Court of Appeals for the Tenth Circuit continued this trend. See Rivera v. Exeter Finance Corp., 2020 WL 6844032 (10th Cir. 2020). In Rivera, “[i]n his second attempt at class certification, Rivera submitted a list of 482 names to the district court.” Id. at *1. “That list was it.” Id. With only this list, the district court denied class certification.

On appeal, the Tenth Circuit affirmed:

Submission of a list of names is not in and of itself fatal to class certification, but failure to also define the class is. . . . [D]efining the class from scratch is not the district court’s job. It is the burden of the plaintiff seeking class certification[.]

Id.

This opinion further solidifies what federal courts have held for over a decade: class definitions matter. While Federal Rule of Civil Procedure 23 does not explicitly place requirements on a plaintiff in defining a class, it does require that “[a]n order that certifies a class action must define the class.” Fed. R. Civ. P. 23(c)(1)(B).

Rivera makes clear that district courts are not going to do the work themselves. Instead, the plaintiff must adequately define the class. And, plaintiffs do not have the freedom to “put the cart before the horse” and provide a district court with a list of names without an adequately defined class. 2020 WL 6844032 at *1.

As defendants defend against class action lawsuits, they must consider challenging the plaintiff’s class definition as not clearly defined. There is more upside – and case law – supporting this tactic than it might at first appear.