Rule 23 Requirements
The federal rule that sets the threshold prerequisites and category-specific tests a proposed class must satisfy before a court will certify it.
Rule 23 is the backbone of federal class action practice. Rule 23(a) sets four prerequisites every class must meet — numerosity, commonality, typicality, and adequacy of representation. A class that fails any one of the four cannot be certified, regardless of how strong the underlying claims are.
Once the 23(a) prerequisites are met, the class must also fit one of the categories in Rule 23(b): injunctive or declaratory relief classes under (b)(2), limited-fund classes under (b)(1), or, most commonly in damages cases, classes where common questions predominate over individual ones and a class action is the superior method of adjudication under (b)(3).
Juricratic models certification as a discrete, high-leverage decision point in the matter's state, because it is often outcome-determinative: a certified class multiplies exposure and settlement pressure by orders of magnitude relative to individual claims, which the simulation reflects directly in the exposure distribution once a certification dial is set.
How it actually shows up
Both sides build their certification strategy around Rule 23's specific text — plaintiffs frame the class definition and common proof to satisfy each element, while defendants target the weakest element, often typicality, adequacy, or predominance, in their opposition.
- What are the four requirements of Rule 23(a)?
- Numerosity (the class is too large for individual joinder to be practical), commonality (common questions of law or fact), typicality (the representative's claims are typical of the class), and adequacy (the representative and counsel will fairly protect the class).
- What is the difference between Rule 23(b)(2) and 23(b)(3)?
- 23(b)(2) covers classes seeking uniform injunctive or declaratory relief; 23(b)(3) covers classes seeking damages and additionally requires that common questions predominate over individual ones and that a class action be the superior method of resolution.
- Can a class be certified for some claims and not others?
- Yes. Rule 23(c)(4) allows certification of particular issues within a case even when the case as a whole would not qualify for full class treatment.
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