Opinion of the Court
A
The only statutorily protected characteristic at issue in today’s cases is “sex”—and that is also the primary term in Title VII whose meaning the parties dispute. Appealing to roughly contemporaneous dictionaries, the employers say that, as used here, the term “sex” in 1964 referred to “status as either male or female [as] determined by reproductive biology.” The employees counter by submitting that, even in 1964, the term bore a broader scope, capturing more than anatomy and reaching at least some norms concerning gender identity and sexual orientation. But because nothing in our approach to these cases turns on the outcome of the parties’ debate, and because the employees concede the point for argument’s sake, we proceed on the assumption that “sex” signified what the employers suggest, referring only to biological distinctions between male and female.
Still, that’s just a starting point. The question isn’t just what “sex” meant, but what Title VII says about it. Most notably, the statute prohibits employers from taking certain actions “because of” sex. And, as this Court has previously explained, “the ordinary meaning of ‘because of’ is ‘by reason of’ or ‘on account of.’” University of Tex. Southwestern Medical Center v. Nassar, 570 U. S. 338, 350 (2013) (citing Gross v. FBL Financial Services, Inc., 557 U. S. 167, 176 (2009); quotation altered). In the language of law, this means that Title VII’s “because of” test incorporates the “‘simple’” and “traditional” standard of but-for causation. Nassar, 570 U. S., at 346, 360. That form of causation is established whenever a particular outcome would not have happened “but for” the purported cause. See Gross, 557 U. S., at 176. In other words, a but-for test directs us to change one thing at a time and see if the outcome changes. If it does, we have found a but-for cause.
This can be a sweeping standard. Often, events have multiple but-for causes. So, for example, if a car accident
