In my latest FindLaw column, I use the botched oath as a vehicle for exploring the differences between the jurisprudential philosophies of President Obama and Chief Justice Roberts. Here I want to expand on a tangential point I make in the column: the purposes oaths serve.
In a trial and some other contexts (like filing a tax form), witnesses and others swear an oath to tell the truth. The oath then subjects the oath-taker to criminal prosecution for lying. However, this is merely the way we have chosen to structure the law. Neither due process nor any other constitutional principle would be offended by a law that criminalized lying in any particular setting, even absent an oath. For example, prosecution for lying to the FBI does not require that the liar have taken an oath to tell the truth in advance.
So why require an oath at trial and in other contexts? Presumably, for at least two reasons: First, to warn and remind the oath-taker of the possibility of prosecution for perjury; and second, to impress upon the oath-taker the seriousness of the occasion, quite apart from any fear of prosecution. Whether the oath actually advances either of these aims is questionable. So too is a third reason that has sometimes been invoked for requiring oaths: that liars and other disreputable people will be unwilling to take the oath. It is hard to imagine that there are a lot of people who would be willing to lie while not under oath but are not willing to lie in an oath. And remember, we can't say that the willingness depends upon the possibility of prosecution, because we could criminalize the lie even without the oath.
The foregoing analysis applies as well to loyalty oaths. The people who, during the McCarthy era and at other times, were too scrupulous to recite a loyalty oath were unlikely to be actual Communist agents working to overthrow the government.
So perhaps the point of the oath is to harness religious obligations to secular ends: There might be some people who would be willing to lie, even at the risk of prosecution, without an oath, but would be unwilling to do so after having sworn to God that they would not. Fear of prosecution is one thing; fear of eternal Damnation is something considerably worse. Here too I'm skeptical of the actual efficacy of oath-taking. Even without the oath, religious people in the three Mosaic faiths are already under the obligation, "Thous shalt not lie." Willingness to violate the scriptural injunction standing alone probably connotes willingness to violate the same injunction coupled with a promise to the Almighty.
Thus, it seems that the principal actual function of an oath, in any context, is simply to solemnify the occasion on which it occurs. It has the added and unfortunate side effect, however, of sometimes weeding out for persecution those people (e.g., Quakers, Jehovah's Witnesses, some pacifists) who do not agree with the oath but are too scrupulous to recite it anyway. Perhaps we'd be better off dispensing with oaths and just training everybody to read microexpressions.
Posted by Mike Dorf