The First Amendment to the U.S. Constitution states, in part, that “Congress shall make no law respecting an establishment of religion, or prohibiting the exercise thereof.” This two-part protection guarantees not only religious liberty, but also freedom from governmental action that purports to establish or support religious causes. The Establishment Clause, or “establishment of religion” clause, is most often invoked in constitutional challenges regarding separation of church and state, whereas the “free exercise” clause is invoked when challenging governmental interference with personal and fundamental religious freedom. The Fourteenth Amendment makes these protections applicable to the states and subdivisions thereof.
In its purest form, the Establishment clause prohibits the state or federal government from establishing or setting up a church or religion as the official state or federal religion; it is said to provide “a wall of separation between church and state,” in the words of Thomas Jefferson. Several U.S. Supreme Court justices, including prior long-term Chief Justice William Rehnquist, believed that the literal translation of the term meant that it only intended to prohibit the establishment of a single national church or the preference of one religion over another. This interpretation was premised on the historical context of the Constitution being drawn up by colonists fleeing oppression under the national Church of England. But other justices interpret a broader application of the term, to include prohibiting the government from promoting religion in general. This broader interpretation prohibits the government from passing laws that tend to favor or show preference for one or all religions, or tend to force belief or disbelief in any particular religion.
Accordingly, over the years, courts have eked out parameters of what government can or cannot do with respect to religion. For example, courts of law cannot adjudicate religious/ecclesiastical questions, nor can a religious test be used for election to public office. Likewise, providing testimony under oath need not be done by using a Bible and swearing before God; persons may substitute with an “affirmation,” a solemn declaration that does not invoke or mention God.
However, in reality, constitutional challenges invoking the Establishment clause tend to be more complicated and/or subtle. Judicial interpretation of the Establishment clause is an ever-evolving area of law, made more so in the 20th and 21st centuries because of the increasing cultural and ethnic diversity of the American population, as well as advancement in scientific technology that speaks to creationism and evolution.