The lone argument on Wednesday, Halliburton Co. v. Erica P. John Fund, presents the kind of question the Justices don’t often consider: “Whether the Court should overrule or substantially limit the holding of Basic Inc. v. Levinson, 485 U.S. 224 (1988).” But the Justices granted the petition to decide that question, and so the focus of argument on Wednesday will be an unusual one: not whether the Court’s existing precedent suggest a decision one way or the other, but whether the Court should jettison the existing precedent entirely.
The case involves the so-called “fraud-on-the-market” theory of liability in a class action under SEC Rule 10b-5.  Because the private right of action under Rule 10b-5 (at least traditionally) has been understood to require reliance, it is difficult to bring a class action based on public misrepresentations about a stock. Among other things, conventional methods of proof might require proof that each of the plaintiffs that purchased the stock was aware of the misrepresentation. Such a standard would make a class action particularly difficult, because the proof in such a regime would not involve common questions of fact or law, but rather would proceed individual by individual.