Opinion of the Court
they may manifest themselves or whatever other labels might attach to them.
The employers try the same point another way. Since 1964, they observe, Congress has considered several proposals to add sexual orientation to Title VII’s list of protected characteristics, but no such amendment has become law. Meanwhile, Congress has enacted other statutes addressing other topics that do discuss sexual orientation. This postenactment legislative history, they urge, should tell us something. Cf. post, at 2, 42–43 (Alito, J., dissenting); post, at 4, 15–16 (Kavanaugh, J., dissenting).
But what? There’s no authoritative evidence explaining why later Congresses adopted other laws referencing sexual orientation but didn’t amend this one. Maybe some in the later legislatures understood the impact Title VII’s broad language already promised for cases like ours and didn’t think a revision needed. Maybe others knew about its impact but hoped no one else would notice. Maybe still others, occupied by other concerns, didn’t consider the issue at all. All we can know for certain is that speculation about why a later Congress declined to adopt new legislation offers a “particularly dangerous” basis on which to rest an interpretation of an existing law a different and earlier Congress did adopt. Pension Benefit Guaranty Corporation v. LTV Corp., 496 U. S. 633, 650 (1990); see also United States v. Wells, 519 U. S. 482, 496 (1997); Sullivan v. Finkelstein, 496 U. S. 617, 632 (1990) (Scalia, J., concurring) (“Arguments based on subsequent legislative history ... should not be taken seriously, not even in a footnote”).
That leaves the employers to seek a different sort of exception. Maybe the traditional and simple but-for causation test should apply in all other Title VII cases, but it just doesn’t work when it comes to cases involving homosexual and transgender employees. The test is too blunt to capture the nuances here. The employers illustrate their concern with an example. When we apply the simple test to Mr.
