Justifications, Excuses, and Affirmative Defenses
本文从经济学角度分析积极抗辩如何通过避免不必要惩罚产生社会效益，并探讨平衡这些效益与轻率抗辩社会成本所需的证据标准，解释了美国各州在证明标准上的差异。
Abstract A defendant who admits to having committed an offense may nevertheless be acquitted if he can provide a legally cognizable justification or excuse for his actions by raising an affirmative defense. This article explains how affirmative defenses generate social benefits in the form of avoided unnecessary punishment. It then asks what kind of evidentiary standards must be used in order to balance these benefits against potential social costs arising from frivolous defense claims. It thereby provides an economic rationale for the uniformity across US jurisdictions in allocating the burden on the prosecution to prove the commission of the offense, as well as the variation across states in the standards of proof they use in determining the validity of affirmative defenses. The analysis also explains why mere assertions of undeterrability should not be considered as affirmative defenses.