In an antitrust case decided on May 21, 2007, the United States Supreme Court abandoned a fifty-year-old liberal pleading rule in favor of a significantly tougher standard applicable to all civil cases that may make it more difficult for plaintiffs to sue and easier for defendants to end lawsuits early, avoiding expensive litigation. The Court's rejection of the old standard is unequivocal: the court's old formulation, quoted for half a century in numerous opinions of the Supreme Court and the lower courts, "is best forgotten as an incomplete, negative gloss on an accepted pleading standard."

In Bell Atlantic Corp. v. Twombly the plaintiffs, Twombly and others, alleged that regional telephone companies such as Bell Atlantic (now Verizon), the so-called "Baby Bells," violated the antitrust laws by illegally conspiring to limit the ability of new local phone companies to compete to provide local telephone services and agreeing not to compete in each other's existing service areas. The plaintiffs alleged that the Baby Bells had engaged in parallel business conduct and that the defendants had agreed to engage in that conduct, but did not allege specific facts relating to that agreement. Because similar businesses often engage in similar conduct without colluding because it is in each business's self-interest to do so, the mere existence of parallel conduct does not violate the antitrust laws. Instead, a plaintiff seeking to show that parallel conduct is unlawful must show additional facts, known as "plus factors," such as communications regarding the parallel conduct or an actual agreement among the defendants to act in concert. The plaintiffs in this case alleged no such facts in their complaint other than the conclusory allegation that the defendants did in fact agree to exclude new telephone companies and not to invade each other's territories.

The District Court quickly dismissed the complaint before discovery had started, and before the defendants had even answered the complaint, because the plaintiffs had not alleged any plus factors necessary to conclude that the alleged parallel conduct violated the antitrust laws. The plaintiffs appealed, and the Court of Appeals reinstated the complaint, concluding that although a plaintiff must prove the existence of plus factors in order to prevail at trial, plus factors need not be pleaded in a complaint. The defendants then turned to the Supreme Court.

The Supreme Court could have concluded that the complaint was insufficient because it failed to allege the required plus factors. Such a holding would have been important for one type of antitrust cases, namely those that allege that defendants' parallel conduct violated the antitrust laws. But the Supreme Court went much further, adopting a new pleading rule that is likely to affect a wide range of civil cases.

For fifty years, courts have evaluated all civil complaints under the standard set forth in Conley v. Gibson, 355 U.S. 42 (1957), which allowed cases to proceed through the process of pre-trial discovery unless, based on the claims alleged in the complaint, the plaintiff could prove "no set of facts in support of his claim which would entitle him to relief." This meant that under Conley, a case brought under the labor and employment laws, a plaintiff needed only to make allegations that put defendants on notice of what the plaintiff's claims were without asserting all of the facts that supported the plaintiff's conclusion that the law had been violated. As long as some set of facts might exist to support the plaintiff's conclusions, the case could go forward. But in Twombly, the Supreme Court rejected this standard, noting that it has "earned its retirement."

The Supreme Court's new standard asks not whether it is conceivable that some set of facts could be developed to support the allegations in the complaint, but rather whether the plaintiff has stated enough facts in the complaint to allow a court to conclude that it is plausible that the plaintiff is entitled to relief. Thus, defendants can avoid the costs and burden of responding to a complaint and to a plaintiff's request for discovery by convincing the judge that the plaintiff's claims are implausible even if they might be remotely possible. Conley was not an antitrust case, and the Court's rejection of Conley was not limited to antitrust cases. It is likely, therefore, that this new pleading standard will be adopted in civil cases generally.