The now-famous metaphor of a "wall of separation" which is often used to describe this principle is not found in the Constitution, but rather in a letter written by Thomas Jefferson to the Danbury Baptist Association in 1802:

"I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should make no law respecting an establishment of religion, or prohibit the free exercise thereof, thus building a wall of separation between church and state."

While it is often argued by accomodationists that this was merely Jefferson's opinion, and that the Founders intended no such "wall", this is proved false by an examination of the history of the first amendment and a series of proposed alternate wordings (that would have merely prevented the government for establishing preference for any one denomination) that were ultimately rejected.