Oath to God is a License to Lie Under Law
Government courts in the U.S. may require secularly affirming truthfulness in order to be able to apply anti-perjury law to a violation of a duty of truthfulness but, in my opinion, may not require some kinds, perhaps any kinds, of oaths of truthfulness for that purpose. Because, in my view, the oaths in question have a religious element without which the oath is facially invalid, it, generally when a lay person required to give the oath is unpersuaded of its lay meaning and of the supremacy of the lay meaning over any theological meaning, is entirely invalid.
The conception of God here applies to any equivalently supreme metaphysical authority in any religion that is accepted for the oath (or an equivalent oath, which is considered herein as arguendo the same).
Theology Unreliable as Authority
Anyone can have any religious belief they wish. This includes a subtle variation from someone else’s belief. Thus, in understanding the meaning and applicability of an oath, sources such as a Bible are useless. Only the person themself is an authority on point, and understanding the intricacies of one person’s religious belief may take too long to be practicable.
An argument is that the theology doesn’t matter when enforcing the law of perjury. But that depends on detecting a secular violation.
We tend to assume that a religious person would not lie after giving an oath. But that depends on theological presumptions about that individual person, presumptions that may not be testable, may not be consistent over time, and need not hold in the face of secular events.
God as Not Existing
In testing the validity of the oath, the first premise to be tested is this: God does not exist. God is merely imagined in many humans’ minds.
You do not have to agree with that premise. That the premise exists is enough.
Given the premise, an oath to God to testify exclusively truthfully is an oath to no one to so testify. An oath to no one is, effectively, not an oath (nor is it an affirmation). That oath is null and void.
Therefore, if the oath is required for a lie to be unlawful, lying against the oath is not unlawful.
Help From God
A contrary argument is that an oath ends with this declaration by the one swearing the oath: “So help me God.” If it does and if the role of God is only to help, then God’s nonexistence does not alter the swearer’s obligation under the oath as a whole.
However, that is not the entire role of God. The rest of the oath is a promise to God [ck]. The whole oath is thus a mutual assistance pact submitted by one party and not necessarily accepted by God, unless under a prior blanket acceptance promulgated by the deity.
The Meaning of “God” For an Oath
If God is omnipresent, as several theologies with large followings assert, an oath to God by one for whom God does not exist approved by one for whom God does exist is a contradiction. It is an oath to God by one who does not believe in a God approved by one who does believe in a God. If the oath is required for a lie to be unlawful, unlawfulness requires belief in a God. If unlawfulness is determined by the government, then a proscription on the government establishing a religion to be agreed with by anyone making the above oath is a proscription on the government finding unlawfulness because of a violation of an oath to God. That proscription is in the First Amendment to the Constitution.
The problem is not limited to atheists and agnostics. It applies also to, for example, to Buddhists, Hindus, and, I think, American Indians of some tribes, insofar as they do not believe in a God as singular and as superior to all other authority, because lack of that belief means that, for them, God is not singular or is not superior to all other authority, thus, in some cases, allowing the oath-giver to obey some perhaps-undefined lawful authority higher than God in contradiction to any duty to God.
The problem may also apply to Muslims. While some theologians state that the God recognized by Christians and the God, named Allah, recognized by Muslims is the same God, some theologians state that the one God is different from the other God.
I do not know if any theologians disagree as to the God, named Yahweh or G-d, recognized by Jews being the God recognized by Christians.
I do not know if theologians disagree as to the God recognized by some Christians and the God recognized by other Christians.
Theological vs. Secular Law
The theology subscribed to by the believer is up to the believer. Law protects religious freedom, including the choice of theologies. It is not necessary for the belief to be approved by anyone else. One can believe in a Roman Catholicism contradicted by the Pope. That is a right in law. It’s probably not the law enforced by the Pope or the Church even in the U.S., but it is a right under U.S. law, including for everyone and regardless of how U.S. law would accommodate a given belief, if at all.
That may be a conflict between two bodies of law. But the Constitutional law is higher than the law of judicial or administrative procedure. Since adjectival law would not fail in its purpose if it did not rely on a theological underpinning, the conflict can be removed by grounding adjectival law on an entirely nontheological foundation.
Education Contrary to Faith
Religion is, by definition, grounded on faith. Much else in secular life is not. Science is not.
Faith denies its followers the right to question the content of the faith or the people who require faithfulness. The followers who question against authority thereby violate their duty to refrain from questioning. We are all taught never to violate any duty, even if there is disagreement on what duties someone has. We are all so taught during almost all of our waking hours we spend with other people. We are all so taught from babyhood and continuously since then.
Law that is secular is often in conflict with a given faith. Law that is theological but of a different theology than that of a given faith community is often in conflict with that faith.
To require a person to obey a secular law contrary to a theological law may lead the person to perceive a conflict between two laws. This may require education on the legal relationship between the two laws.
But when the person has had an education to obey faith and received that education during most waking hours and during most years from babyhood to the current time, an education which is usually complex and progressive through intellectual stages, and then receives a few minutes of contrary education, it is almost impossible for the explainer of the contrary to refute the complex earlier education on duties from faith.
People often encounter many conflicts between new and old education; but they often resolve those conflicts by finding ways to conform one to the other. In this situation, one way is to obey the oath by obeying a duty to God and thereunder obeying a duty to people in accordance with the duty to God.
That would be in conflict with secular law, but the explainer of secular law with only a few minutes for the explanation may not have time to counter that kind of conformance. The person then will likely believe the conformance is correct.
Duty to God
A duty to God may theologically require a duty to people. The two duties may differ, because, in the U.S., secular law need not regulate theological law. But, in the U.S., secular law is superior to theological law. So, while the two bodies may conflict, when they conflict what purports to be the inferior law is not law in that circumstance, and therefore theological law in conflict with secular law is not law, leaving only the secular law as law for the circumstance.
But a lay person may not understand that and it may never be taught to the person, especially at the moment when the knowledge about the conflict is needed. The person may have been taught the opposite by other theologically-minded people, even though the opposite is erroneous under society’s law and sometimes leads to personal liability under secular law.
And the lay person may understand or interpret their duty to God or other theological duty as imposing a duty with respect to people that contradicts what a court demands as the duty to people. That may be applied by the lay person in question so that they lie in their testimony in the belief that the lie is required by an authority higher than that of the court.
The oath may be permission to lie.
That is the danger of the oath. Even perjury law or the law of contempt of court may be inapplicable if the oath constitutes, or may reasonably be understood as, permission or even a duty to obey theological duties that are not defined in secular law. The oath may create an exception that would make secular enforcement impossible.
In the U.S., Christianity is, by far, the most populous religion, and probably the most populous religious belief, if atheism and agnosticism are religious beliefs but not religions. It appears that it is commonplace for government courts in the U.S. to state “In God We Trust” and thereby reference Christianity and any religion in agreement with that aspect of Christianity. Therefore, the unconstitutionality is in the virtual establishment of Christianity as a state religion, virtually because while no government order may have required agreement with Christianity it does, under pain of imprisonment, require behavior in agreement with Christianity or with a religion in agreement with Christianity, specifically the giving of an oath.
Religious courts, of course, insofar as subject to religious law, may require oaths consistent with the religions governing such courts, but, in the U.S., such courts are not government courts. If a government in the U.S. were to rely on a decision of a religious court in turn relying on such an oath, such reliance by the government would be unconstitutional.
Religion depends on faith that may not be challenged by a human follower except with permission of a human leader. That contradicts the right of people, using lawful means, to seek changes in law or to challenge a legal judgment through due process that is for determining facts for the application of law. Therefore, acceptance of a religion must not be required of someone seeking so to change law or so to challenge a legal judgment.
The Constitutionality is with respect to the First Amendment.
Affirming Proper Legal Relationships
Government, including its courts, must be run on the basis that people who are constituents (generally, nationals of the nation wholly or partly governed by the government regardless of where in the universe such nationals are located, all other individuals who are present in the jurisdiction of such government, and individuals sufficiently associated with any entity subject to the jurisdiction of such government) are responsible to that which exists and not to that which does not exist.