In the late eighteenth century, American law treated oath-taking as an invocation of divine vengeance for sworn falsehoods. Prospective witnesses who did not believe in God or hell were not allowed to testify. But this strict evidentiary rule survived only a few more decades. Gradually at first, and then with growing speed, the theological underpinnings of oath-taking eroded across the United States in the early nineteenth century. The story of this transition, only vaguely appreciated in the current literature, illuminates and weaves together several important strands of nineteenth-century social and legal history. The common-law rule, it turns out, came into escalating conflict with American religion, particularly after a liberal offshoot of Calvinism began rejecting the existence of hell. By prevailing founding-era standards, being unable to testify did not impede or punish the exercise of religion, allowing the rule to survive an initial volley of legal challenges. But as reform efforts mounted, a neutrality-based view of religious liberty and an egalitarian conception of civil privileges began to supplant the earlier constitutional settlement. By the mid-nineteenth century, evidence rules throughout the United States no longer required belief in hell, and almost half of the states allowed atheists to testify. This transition also prompted the first widespread rethinking of American evidence law, shifting its foundational principle from reliance on the inviolability of oaths to confidence in the jury's fact-finding capacity, and laying the groundwork for further liberalization in the 1850s and 1860s that allowed testimony from black witnesses and from interested parties. Moreover, the controversy about religion-based exclusions led to a new understanding that barring testimony from particular minority groups effectively denied those groups the protection of the law.
