What should a defendant do to prove their affirmative defense?

To establish an affirmative defense, a defendant is required to prove their case by a preponderance of evidence. This standard means that the defendant must show that their argument is more likely true than not—essentially, that there is greater than a 50% chance that the claims made in the affirmative defense are valid. This is a lower burden of proof compared to other legal standards, such as "beyond a reasonable doubt," which applies in criminal cases to establish guilt.

In the context of the legal system, the preponderance of evidence is commonly used in civil cases or situations involving affirmative defenses, as it reflects a balance of probabilities rather than an absolute certainty. This allows a defendant to effectively argue for their defense based on evidence, testimony, and relevant facts, rather than needing to provide irrefutable proof. Other options such as clear and convincing evidence or proof beyond a reasonable doubt set higher thresholds that are not required in the context of proving affirmative defenses. The choice that restricts proof to testimony only also limits the types of evidence that can be presented, whereas various forms of evidence—such as documents, physical evidence, and witness statements—can support establishing an affirmative defense.