A Tort-Based Causation Framework for Antitrust Analysis

Causation is one of the most underexplored areas in antitrust law. What must a plaintiff show to connect a defendant’s conduct with anticompetitive effects? Several tests are possible, including “but for” causation, proximate cause, sole causation, reasonable connection, and increased possibility of harm. Courts have applied variations of all these tests. This article focuses on the two settings in which the issue of antitrust causation has most often arisen: monopolization cases and, more generally, cases addressing antitrust injury. Some of the most difficult causation issues occur in monopolization cases. One such issue involves determining the counterfactual scenario of what would have happened absent the monopolist’s conduct. A second occurs when both the monopolist’s actions and other events cause the injury to competition. In this setting, courts have diverged on whether the presence of other causes precludes a finding of monopolization. In dynamic high-technology markets, these issues are even more challenging. It is not easy to hypothesize the path not taken in a rapidly changing market or to separate the effects of the monopolist’s conduct from those of other events affecting the market’s development. These difficulties are compounded because of the concern of punishing unilateral conduct and because the standards articulated by courts in monopolization cases are often not clear. The second antitrust setting in which courts have frequently addressed causation is the analysis of antitrust injury. The Supreme Court and lower courts have famously explored whether a plaintiff suffers injury “of the type that the antitrust laws were intended to prevent and that flows from that which makes the defendants’ acts unlawful.” This inquiry is designed to ensure that the plaintiff is able to show harm to “competition not competitors.” This article examines these causation issues and gains insights by turning to tort law, the law with the most developed causation framework. It focuses on two core concepts of causation in tort law, factual and legal cause. As exported to antitrust law, the tort factual cause inquiry would ask if a plaintiff can show a “reasonable connection” between the challenged conduct and the anticompetitive effects. This range of potential causes is limited by the requirement of legal causation, which would determine if a plaintiff’s harm results from anticompetitive — as opposed to other — conduct