Precisely what this means is a matter of controversy. I disagree with the position take by one commentator about the issue that "it has long been understood that Rule 8 requires pleadings to contain allegations in support of each material element of a claim."
Pleading all elements of a claim was not the law before Twombly, and is not the law even after Twombly, which required something short of that standard.
Indeed, the fact that one need not plead all elements was emphatically reiterated in the 7th Circuit just before Twombly was announced by Judge Easterbrook in Vincent v. City Colls. of Chicago, 485 F.3d 919, 923 (7th Cir. 2007) ("Any decision declaring ‘this complaint is deficient because it does not allege X’ is a candidate for summary reversal, unless X is on the list in Fed. R. Civ. P. 9(b).")
Similarly, as the Twombly court notes at slip op 23: "Swierkiewicz v. Sorema N. A., 534 U. S. 506, 508 (2002) . . . held that "a complaint in an employment discrimination lawsuit [need] not contain specific facts establishing a prima facie case of discrimination under the framework set forth in McDonnell Douglas Corp. v. Green, 411 U. S. 792 (1973)." And, the Twombly court makes clear that it is not reversing Swierkiewicz.
The distinction Twombly seems to make is not over how many facts must be provided or how specific they mus be, but instead concerns what counts as a factual allegation in a Complaint.
Twombly at slip op. 8 gets to the heart of the matter by saying (emphasis added and some citations omitted):
While a complaint attacked by a Rule 12(b)(6) motion to dismiss does not need detailed factual allegations . . . a plaintiff's obligation to provide the "grounds" of his "entitle[ment] to relief" requires more than labels and conclusions, and a formulaic recitation of the elements of a cause of action will not do, see Papasan v. Allain, 478 U. S. 265, 286 (1986) (on a motion to dismiss, courts "are not bound to accept as true a legal conclusion couched as a factual allegation").
The allegations in the anti-trust case before it fail not because elements of the claim necessary to make out a prima facie case are omitted. The Complaint alleges that all material elements of the claim are present, including an allegation, made upon information and belief, that the agreement which must be shown to prevail exists. The Complaint is insufficient, instead, because the Plaintiff's language regarding the core issue of the existence of an illegal agreement isn't factual enough to constitute a genuine factual allegation. The key allegation that wasn't good enough in Twombly said:
In the absence of any meaningful competition between the [ILECs] in one another's markets, and in light of the parallel course of conduct that each engaged in to prevent competition from CLECs within their respective local telephone and/or high speed internet services markets and the other facts and market circumstances alleged above, Plaintiffs allege upon information and belief that [the ILECs] have entered into a contract, combination or conspiracy to prevent competitive entry in their respective local telephone and/or high speed internet services markets and have agreed not to compete with one another and otherwise allocated customers and markets to one another.
In other words, the Complaint in Twombly failed because the Plaintiffs only speculated that it seemed like an illegal agreement existed without having more than vague circumstantial evidence that didn't point "plausibly" in the words of the Twombly court to this conclusion in the absence of any corroborating allegations that there was really an agreement out there. If one bases a complaint not on what you know, but on information and belief, the "information" you do have that provides a basis for your "belief" must plausibly imply what you believe but do not know to be the case.
While you don't have to know all the details of the agreement, you need to have more than a mere hypothesis that this core element of an anti-trust case is out there.
As the Twombly court explains at slip op. 24: ""we do not require heightened fact pleading of specifics, but only enough facts to state a claim to relief that is plausible on its face."
Erickson v. Pardus, a Colorado case decided by the U.S. Supreme Court a month later, alleging lack of medical treatment dismissed on the pleadings because the harm suffered was not very specifically described by an unrepresented inmate, reemphasized the notion that as long as on is speaking the language of facts and not mere conclusions of law disguised as facts, that one need not be too specific and detailed to state a claim that is sufficient for further court action on its face.
Twombly and Pardis also both consider what is at stake in the case on the merits and who is doing the pleading. The Court implicitly recognizes in these cases that the distinction between a specific fact, a fact, and a mere legal conclusion, flows from context. In an extraordinarily large and complex class action case brought by specialist lawyers, counsel should be offered little slack because of the stakes involved in allowing half baked cases to go forward. In a simple case brought by a simple man, more reading between the lines is permissible.
Here too, plausibility is the guide. The justices are skeptical in Twombly because the inference made from "information" to the belief that there is an illegal agreement by the Plaintiffs is thin and can be explained many other ways that also make sense. The justices are more willing to accept the allegation made in Pardis because substantial harm is a natural and plausible consequence of denying an inmate treatment for a deadly disease.
A Complaint may legitimately require a judge to fill in some blanks that likely follow from context, but cannot demand that a judge make the same factual inferences that the Plaintiff does, if the judge finds it hard to swallow inferences the Plaintiffs offer.
Once upon a time, pleading rules and rules regarding expert opinions prohibited complaints and expert witnesses from offering up "ultimate facts" or bare legal conclusions. Only "real facts" were allowed. For half a century, that requirement was rolled back - ultimate facts and legal conclusions were good enough. Twombly is best viewed as a restoration of the ultimate facts rule. Complaints may now include ultimate facts and legal conclusions to guide the reader, but ultimate facts and legal conclusions by themselves are insufficient by themselves to state a claim. Instead, Complaints must now offer up a core of real facts that show that there is a plausible basis for the grievance, even when the ultimate facts and legal conclusions that frame those facts are stripped away.