Historically test oaths were weapons to inflict penalties and punishments on obnoxious minorities and were enemies of freedom of political and religious thought. A test or LOYALTY OATH should not be confused with an oath of allegiance, which is a promissory oath by which one swears to support the government and, if assuming office, to discharge its duties faithfully. An oath of allegiance concerns future conduct. A test oath is retroactive and purgative, because it is a disclaimer of specific beliefs, associations, and behavior deemed criminal or disloyal.
Missouri by its constitution prescribed a series of disavowals of belief and past conduct in the form of oaths to be taken by all voters, jurors, state officers, clergymen, lawyers, teachers, and corporation officers. All must swear as a condition of voting, holding office, teaching, and the like, that they had never been in armed hostility to the United States, had never by word or deed manifested adherence to the enemies of the country or desired their victory, had never been connected with any organization inimical to the United States, and had never been a Southern sympathizer. Anyone teaching, preaching, voting, or engaging in any of the specified activities without first taking the oaths was subject to fine and imprisonment. Cummings, a Roman Catholic priest, carried on his religious duties without taking the oath and was convicted.
The test oath prescribed by Congress was a disclaimer of having served the Confederacy and applied only to federal officials until extended in 1865 to members of the federal bar. It could be construed as a wartime qualification for office until it was extended to peacetime and to members of the federal bar. Until then it was not passed to inflict punishment for past offenses. The oath disqualified AUGUSTUS H. GARLAND, who had spent the war as a member of the Confederate Congress, from resuming his prewar practice before the Supreme Court, although he had been given a presidential pardon.
The Supreme Court, Justice STEPHEN J. FIELD writing for a bare majority, held unconstitutional both the Missouri requirement of a test oath and the federal requirement of 1865. Field reasoned that each violated the bans against EX POST FACTO laws and BILLS OF ATTAINDER. To conclude that they constituted ex post facto laws, Field had to demonstrate that they retroactively imposed punishment for acts not criminal when committed. Missouri's...