The law of ascertainability at class certification is straightforward. A class definition satisfies Rule 23’s implied ascertainability requirement if the class is defined by reference to objective factors and it is administratively feasible to determine whether a particular individual belongs to the class. As summarized in the Manual for Complex Litigation, a class definition must “avoid subjective standards (e.g., a class member’s state of mind) or terms that depend on resolution of the merits (e.g., ‘persons who were discriminated against’).” Manual for Complex Litigation (Fourth) § 21.222, at 270 (2004).
There are several sound reasons for the ascertainability requirement. First, courts require classes to be defined in a clearly ascertainable manner to identify who must receive notice of class certification under Rule 23(c)(2). Second, the definition of an ascertainable class will identify who will be bound by any judgment, thus avoiding subsequent litigation over a judgment’s preclusive effect. Third, the ascertainability requirement ensures it will be feasible to identify class members who may ultimately be entitled to damages or other relief. Defining class membership by reference solely to objective factors also avoids fail-safe classes, in which a class is defined in terms of the merits of a plaintiff’s claims. Members of a fail-safe class can be identified only after the defendant has been found liable, meaning that a favorable ruling will apply only to the plaintiff and not to the class, in addition to making class notice impossible.