The 116th Congress will be sworn in tomorrow. Most members will take the oath of office on a Bible, but some will not.

Members get to decide for themselves. Contrary to popular belief, nothing in the Constitution requires members of Congress, the president, cabinet officials or any federal official to swear their oaths of office on Bibles. Many do so, but it’s just tradition. It’s not required.

This issue comes up every now and then. Some people are convinced that Bibles must be used. In December 2017, Ted Crockett, a spokesman for unsuccessful U.S. Senate candidate Roy Moore, appeared on CNN and defended Moore’s position that Muslims should not be allowed to hold public office. Crockett said this was so because, “You have to swear on a Bible to be an elected official in the United States of America.”

When host Jake Tapper pointed out that this was not true, Crockett just stood there with his mouth hanging open. It was news to him.

Three Muslims will be sworn in tomorrow (along with members of other non-Christian faiths), so it’s likely this issue will surface again. Here’s what you need to know:

The Constitution mentions oaths of office twice. Article VI, Section 3 deals with members of Congress. It reads, “The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution. …”

Article II, Section 1 pertains to the president. It says, “Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation: ‘I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States.’” (Note that the phrase “So help me, God” is not part of the oath. The words are often added, but again, it’s just tradition.)

That’s it. There’s no mention of what you’re supposed to swear on. Sure, members can use a Bible, but they’re not required to use anything. They can just take the oath if they choose. Or they can swear on another book. U.S. Rep. Keith Ellison (D-Minn.), whose term ends tomorrow, took his first oath of office on a Quran owned by Thomas Jefferson. Other members have taken oaths on copies of the Constitution (which seems appropriate). Commentators have mentioned the possibility of swearing on a Shakespeare play, a graphic novel or a book of poetry.

For members of Congress, the rule is to take the oath however you like. And remember, when folks tell you that our officials have to use a Bible, they’re simply wrong. What’s more important is that elected officials are by oath bound to defend the Constitution – not a religious book they might for a moment have their hand on.