Because legal determinations often turn on motive, and motives are often complex, courts must decide what to do about mixedmotives. For example, a boss might fire someone both for lawful reasons relating to job performance and also because of illegal prejudice. Increasingly, courts evaluate such cases under a “But-For standard,” which finds for the plaintiff only if the defendant would have acted differently but forthe bad motive. Put another way, the defendant loses unless the bad motive made some kind of causal difference in outcomes. While this approach is intuitive, I argue that the But-For standard is problematic. The widespread acceptance of the But-For standard is the most important failure in our jurisprudence of mixed motives.