106 Iowa L. Rev. 483 (2021)
Standards of causation in antidiscrimination law, and disparate-treatment cases in particular, are deeply flawed. Their defects have caused an illogical, obscure, and unworkable proof scheme that requires an overhaul to curb the harm that it engenders and to allow the antidiscrimination statutes to serve their objectives effectively. This Article proposes a theory and method of causation that achieves this goal. The problem stems from the inadequacies associated with current standards of causation in disparate-treatment cases—the but-for test and the motivatingfactor test. The proposed “factorial” approach introduces a causal standard that addresses these inadequacies. It entails three innovations over current causation schemes: (1) it adopts a predominant framework for cause and effect in the sciences, called the “potential-outcomes” framework, as a central structure in which to sharply define and analyze the causal inquiry; (2) it employs a causal measure, called the “NESS” test, that refines and, in a sense, unifies the but-for and motivating-factor tests by retaining the central feature of the but-for test—the “necessity condition”—but in a less restrictive form; and (3) it applies a legal framework grounded in tort law and recent advances regarding multiple sufficient causes. In addition to reflecting actual cause and effect, the proposed approach promotes antidiscrimination law’s deterrence and fairness objectives, and it allows an interpretation of causal language in antidiscrimination statutes that is consistent with good policy and Congress’s intent—an interpretation not possible under current standards.