Class certification under Rule 23 is where most class actions actually live or die. The merits barely matter at this stage. What matters is whether the plaintiff can satisfy a checklist of structural requirements that courts have spent decades arguing about. If you’re on the plaintiff’s side, you need to understand exactly what each element demands. If you’re defending, you need to know where the soft spots are.
The 23(a) Prerequisites: Four Boxes You Have to Check
The rule lays out the baseline requirements this way:
(a) Prerequisites. One or more members of a class may sue or be sued as representative parties on behalf of all members only if:
(1) the class is so numerous that joinder of all members is impracticable;
(2) there are questions of law or fact common to the class;
(3) the claims or defenses of the representative parties are typical of the claims or defenses of the class; and
(4) the representative parties will fairly and adequately protect the interests of the class.
Numerosity is usually the easiest box to check. Courts in most circuits treat 40 or more class members as presumptively sufficient. Below that number, you’re in contested territory. Plaintiffs don’t need to identify every member by name, but they need something more than speculation about class size.
Commonality got significantly harder after Wal-Mart Stores, Inc. v. Dukes. The Supreme Court made clear that a common question means more than pointing to a shared legal theory. Claims must depend on a common contention capable of classwide resolution — meaning that determining its truth or falsity will resolve an issue central to the validity of each claim in one stroke. A single common question can satisfy the rule, but that question has to actually matter to the outcome. Defense counsel regularly press this point now, arguing that even if a common question exists, the answers will differ member by member.
Typicality and commonality overlap substantially, and courts sometimes treat them together. The basic inquiry is whether the representative’s claims arise from the same course of conduct and legal theory as the class claims. The representative doesn’t need identical facts, just enough alignment that pursuing her claim will advance the class claims. Where typicality tends to fail: the named plaintiff has a defense available against her that doesn’t apply to the class (an arbitration clause, a statute of limitations problem, a unique damages issue).
Adequacy has two components that courts analyze separately. First, is there any conflict between the representative’s interests and the class’s interests? Second, is class counsel competent and experienced? Defendants probe this by hunting for intra-class conflicts, particularly in cases where some class members have larger claims or different legal theories than others.
The 23(b) Types: Picking Your Vehicle
Once you clear 23(a), you have to fit the case into one of three types. The choice shapes everything that follows, including whether class members can opt out.
23(b)(1) covers situations where separate adjudications would create inconsistent standards or effectively resolve the rights of absent parties. You see this most often in limited fund cases and cases involving ERISA plan administration. Courts certify these relatively rarely now, and the Supreme Court put significant constraints on the limited fund theory under 23(b)(1)(B) in Ortiz v. Fibreboard Corp.
23(b)(2) is the civil rights vehicle. It requires that the opposing party “acted or refused to act on grounds that apply generally to the class, so that final injunctive relief or corresponding declaratory relief is appropriate respecting the class as a whole.” No opt-out right. Wal-Mart also put constraints here, holding that individualized monetary relief claims can’t piggyback onto a (b)(2) class. If damages are more than incidental, you’re in (b)(3) territory.
23(b)(3) is where most consumer fraud, antitrust, securities, and mass tort class actions live. It’s also where the fights are.
Predominance Under 23(b)(3): Where Cases Are Won and Lost
(3) the court finds that the questions of law or fact common to class members predominate over any questions affecting only individual members, and that a class action is superior to other available methods for fairly and efficiently adjudicating the controversy.
Predominance is not just a restatement of commonality with a higher bar. The analysis is qualitative, not quantitative. The question isn’t whether common issues outnumber individual ones; it’s whether common issues are central to the litigation and would drive resolution of the case. You can have ten individual issues and one common issue, and still have predominance if that common issue is the crux of the case.
That said, the area where predominance most often fails is damages. After Comcast Corp. v. Behrend, plaintiffs need a damages model that measures classwide harm consistent with — and limited to — their surviving theory of liability. The Comcast class ran into trouble not because their model was too narrow, but because it was too broad: after the court accepted only one of their four theories of antitrust impact, their expert’s damages model still accounted for all four. A model that doesn’t isolate harm attributable to the specific theory the court accepted cannot establish that damages are susceptible of classwide measurement. Defense experts now routinely attack plaintiff damages models at the certification stage on exactly this mismatch theory, and district courts have to engage with those arguments rather than defer to the merits.
Circuits have diverged on how far the predominance analysis has to go into merits questions. The Ninth Circuit is generally more willing to certify, reasoning that merits questions should be left to summary judgment and trial. The Third and Fifth Circuits press harder at the certification stage, particularly on causation and damages.
Superiority is the other (b)(3) requirement, and most lawyers don’t spend nearly enough time on it. The rule lists specific factors the court should consider, including the difficulties in managing the class action and the desirability of concentrating litigation in that forum. If your class action is going to require thousands of individualized damages hearings, you have a superiority problem even if you win on predominance.
The Mistake Plaintiffs’ Counsel Make Most Often
Waiting too long to retain experts. Courts now expect a rigorous analysis at certification. In antitrust and consumer fraud cases, you will almost certainly need an expert to establish that common evidence can prove impact on a classwide basis. Showing up at the certification hearing without one, or with an expert whose methodology hasn’t been stress-tested, is how you lose a case you should have won. Get your expert early, make sure she can survive a Daubert challenge, and build your class definition around what her methodology can actually support.
For the interplay between your certification motion and your initial disclosure obligations, see Rule 26. Class cert briefing schedules also frequently intersect with Rule 16 scheduling orders, so confirm deadlines early and build in time for expert depositions before the hearing.