Earlier this week, the Supreme Court issued a decision explaining "but for" causation. Burrage v. United States, 2014 WL 273243 (Jan. 27, 2014) (No. 12-7515).
While this was a criminal case, the Supreme Court construed the meaning of "but for" causation across the entire body of the law, explicitly clarifying its own precedents in employment discrimination law to mean that there can be more than one but-for cause. In discussing its prior opinions in University of Tex. Southwestern Medical Center v. Nassar, 133 S.Ct. 2517, 2528 (2013), slip opinion at 11-12, and Gross v. FBL Financial Services, Inc., 557 U.S. 167, 176 (2009), it quoted Nassar and Gross but substituted a bracketed "[a]" for the word "the" preceding the expression "'but for' cause." Accordingly, "but for" causation does not require a showing that an impermissible motive was the sole cause of the challenged action."