What is ascertainability?

Ascertainability is an implied requirement, recognized in some federal circuits, that a proposed class be defined using objective criteria that make it administratively feasible to identify who is actually in it. Courts split on how strictly to apply it: the Third Circuit requires a reliable, low-burden identification method, while the Sixth, Seventh, Eighth, and Ninth Circuits apply a looser standard or reject a freestanding test.

Ascertainability disputes often decide certification in cases involving low-dollar purchases with no receipts, where a class of 'everyone who bought this product' might be easy to define in words but hard to verify member by member. A defendant challenging certification on ascertainability grounds is arguing that even if the class as described is legally sound, there is no workable way to confirm membership at the claims stage. This is a court-level certification issue, not something an individual claimant resolves on their own.

Last reviewed 2026-08-22.