On April 19, 2005, the Supreme Court announced its unanimous opinion in Dura Pharmaceuticals, Inc. v. Broudo, concerning what a plaintiff must show to establish causation in a Rule lob-5 fraud-on-the-market suit for damages. The opinion had been awaited with considerable anticipation, being described at the time of oral argument in the Financial Times, for example, as the most important securities case in a decade. After the opinion was handed down, a representative of the plaintiffs\u27 bar lauded it as a unanimous ruling protecting investors\u27 ability to sue. A representative of the defendants\u27 bar equally enthusiastically hailed it as a significant victory for public companies and others named as defendants in securities fraud cases. This Article seeks to ascertain the opinion\u27s real significance and to provide a framework for resolving the issues that remain open to be decided by future courts. In the tradition of Bob Clark\u27s treatment of Rule lOb-5 issuer misstatement cases, this framework recognizes that these issues involve difficult tradeoffs that defy perfect solutions.
The Supreme Court\u27s grant of certiorari in Broudo v. Dura Pharmaceuticals came against the backdrop of years of highly confusing lower court decisions concerning what a plaintiff needs to show to establish causation in a fraud-on-the-market suit. This confusion had arisen, I will argue, because the lower courts had tried to analyze causation in fraud-on-the-market cases using the twin concepts of transaction causation and loss causation. These concepts had been originally developed in connection with causation determinations in cases based on traditional reliance. Traditional reliance-based cases, unlike fraud-on-the-market cases, involve the plaintiff establishing that defendant\u27s misstatement induced the plaintiff to enter into what has turned out to be a losing transaction. In such cases, transaction causation was satisfied by the very showing of traditional reliance, i.e., that the plaintiff would not have purchased but for the misstatement. Loss causation in these cases involved, in turn, an additional showing that the purchased security declined in value from what was paid (or was sold at a loss) and that the decline or loss was in some way reasonably related to the falsity of the statement that induced the purchase. The function of the loss causation requirement, like the function of proximate cause in actions for negligence, was to prevent the wrongdoer from being responsible for all the consequences for which his action was a but for cause, i.e., all the losses, however unrelated to the misstatement, that the plaintiff might suffer over time as a result of purchasing this security
