Courts use mixed-motive jury instructions in many discrimination and improper retaliation cases. These instructions usually take the following form: "If the plaintiff shows that the defendant did something that hurt her, and the action was motivated by an impermissible reason, there is a presumption that the defendant's conduct was wrong. The defendant may rebut this presumption by showing that it would have taken the action regardless of its impermissible motive."
For example, where an employer fired an employee in part because the employee was an African American and in part because the employee fraudulently overstated her job qualifications, the employer probably would not be liable for illegal racial discrimination, because fraudulently overstating your job qualifications is grounds for firing regardless of race. If, however, the employer fired the employee because of the employee's race and because the employee did not like the Yankees, the employer would probably be liable, because not liking the Yankees is generally insufficient grounds to fire someone. See Employment Discrimination Law; Retaliatory Eviction.
There are several varients to these instructions. Some, such as the example outlined above, trigger a presumption of liability if an improper motive played any part in a defendant's decision. Others require the improper motive to play a significant role in the decision.
In some cases, courts require plaintiffs to show that an improper motive was a "but-for" cause of the defendant's action. This is not a mixed-motive instruction.