Class actions, and Rule 23 of the Federal Rules of Civil Procedure, have long been rife with controversy. It’s safe to assume that the Seventh Circuit’s decision last week in Fonder v. Sheriff of Kankakee Cnty., No. 15-2905 (7th Cir. May 26, 2016), will likely garner mixed reviews from the bar.

Fonder is a reminder that class certifications are not set in stone. Judge Easterbrook—who wrote for the court, joined by Judge Sykes and Judge Adelman from the E.D. Wis., who sat by designation—held that class definitions must be revisited when “evidence calls into question the propriety” of such definitions.

The substantive issue confronted in Fonder stemmed from a class action filed by three arrestees who objected to the constitutionality of a jail’s written policy to “strip search” every arrestee before that person entered the general population. The plaintiffs objected to the policy because it applied to all arrested persons, even those who had not yet been brought before a judge for a probable-cause determination.

The district court certified the class with the following definition: “All persons held in the custody of the Sheriff of Kankakee County from April 20, 2010 to the date of entry of judgment who, following a warrantless arrest, were strip searched in advance of a judicial determination of probable cause.” Relying upon the United States Supreme Court’s holding in Florence v. Bd. of Chosen Freeholders, 132 S. Ct. 1510 (2012), the district court ultimately held that the written policy was constitutional as applied to the defined class.

On appeal the Seventh Circuit criticized two aspects of the district court’s holding.

First, the Court underscored the “mismatch” between the Supreme Court’s rationale inFlorence, which depended upon the arrested person’s placement in the general population, and the class definition certified by the district court, which included all arrestees regardless of whether they entered the jail’s general population. The Court explained that the subset of arrestees subjected to a strip search, but never placed in general population, may have “good claims that their rights have been violated.” However, because those arrestees were included in the class definition, they would be precluded from filing their own lawsuits.

Second, discovery revealed that the jail’s written policy of strip-searching every arrestee before placing them in general population was not consistently applied. Nevertheless, the district court held that “the power to conduct a strip search of every arrestee implie[d] the lesser power to inspect a subset of all arrestees.” The Seventh Circuit disagreed.

Before the Seventh Circuit could effectively remedy the district court’s errors, however, it needed to address the district court’s implied holding that the class waived its opportunity to contest how the written policy actually worked in practice by having proposed a class definition that broadly included all newly arrested persons.

The Court explained that, although Rule 23 requires class certification early in a suit, certifications are nevertheless “tentative.” And, whenever evidence casts doubt upon the propriety of a particular class definition, “the definition must be modified or subclasses certified.” Moreover, just because Rule 23 defines a class early in a lawsuit, it does not justify “adjudicating hypothetical issues rather than determining the legality” of what actually transpired.

As Judge Easterbrook succinctly stated, “[t]he class definition must yield to the facts, rather than the other way ‘round.”