From the ordinary public meaning of the statute’s language at the time of the law’s adoption, a straightforward rule emerges: An employer violates Title VII when it intentionally fires an individual employee based in part on sex. It doesn’t matter if other factors besides the plaintiff ’s sex contributed to the decision. And it doesn’t matter if the employer treated women as a group the same when compared to men as a group. If the employer intentionally relies in part on an individual employee’s sex when deciding to discharge the employee—put differently, if changing the employee’s sex would have yielded a different choice by the employer—a statutory violation has occurred. Title VII’s message is “simple but momentous”: An individual employee’s sex is “not relevant to the selection, evaluation, or compensation of employees.” Price Waterhouse v. Hopkins,490 U. S. 228, 239 (1989) (plurality opinion).
The statute’s message for our cases is equally simple and momentous: An individual’s homosexuality or transgender status is not relevant to employment decisions. That’s because it is impossible to discriminate against a person for being homosexual or transgender without discriminating
against that individual based on sex. Consider, for example, an employer with two employees, both of whom are attracted to men. The two individuals are, to the employer’s mind, materially identical in all respects, except that one is a man and the other a woman. If the employer fires the
male employee for no reason other than the fact he is attracted to men, the employer discriminates against him for traits or actions it tolerates in his female colleague. Put differently, the employer intentionally singles out an employee to fire based in part on the employee’s sex, and the
affected employee’s sex is a but-for cause of his discharge. Or take an employer who fires a transgender person who was identified as a male at birth but who now identifies as a female. If the employer retains an otherwise identical employee who was identified as female at birth, the employer intentionally penalizes a person identified as male at birth for traits or actions that it tolerates in an employee identified as female at birth. Again, the individual employee’s sex plays an unmistakable and impermissible role in the discharge decision.