Courts frequently say that ascertainability is an implied prerequisite to class certification. Yet this requirement rarely receives much judicial attention. Courts are typically drawn to the more familiar — and related — elements of Federal Rule 23. But, a recent decision from the Third Circuit in a consumer class action breathes new life into this lonely element, creating important tactical opportunities in the process. Indeed, ascertainability may be the first, last and only stop for many putative classes. Here's what happened.