Whether an ADEA plaintiff may establish liability under a mixed-motives framework by showing that age was one motivating factor, after which the employer bears the burden to prove it would have made the same decision anyway.
Holding
No. An ADEA disparate-treatment plaintiff must prove that age was the but-for cause of the adverse employment action; the burden of persuasion never shifts to the employer on a same-decision defense.
Reasoning
The Court distinguished Title VII precedent, especially Price Waterhouse and Desert Palace. Congress amended Title VII in 1991 to expressly make an employment practice unlawful when race, color, religion, sex, or national origin was “a motivating factor,” even if other factors also motivated the decision, and to prescribe limited remedies where the employer proves it would have acted the same way. The ADEA contains no comparable language.
Congress amended Title VII's mixed-motives provisions while contemporaneously amending the ADEA in other respects, but it did not add motivating-factor liability to the ADEA. That deliberate difference mattered: the Court would not import a rule from one statute into another when Congress expressly changed one statutory scheme and left the other without the same change.
The ADEA makes it unlawful to take an adverse action “because of” an individual's age. Reading those words according to their ordinary meaning—“by reason of” or “on account of”—the Court concluded that age must be the reason for the challenged decision. Its prior ADEA decision in Hazen Paper likewise described the protected trait as needing to have a determinative influence on the outcome.
Thus, age must be a but-for cause of the action, not merely one factor among several. The plaintiff bears the ordinary burden of persuasion to establish that element by a preponderance of the evidence, and nothing in the ADEA's text creates an exception shifting that burden to the employer in alleged mixed-motives cases.
The Court also noted that Price Waterhouse's burden-shifting framework had proved difficult for courts and juries to administer. Even if that framework were sound under Title VII before Congress amended that statute, those practical problems provided no reason to extend it to a distinct statute that lacks Title VII's motivating-factor language.