By edict of the U.S. Supreme Court, it's illegal to pray at a high school graduation, and you had better not include too many Christmas symbols in the holiday display on the courthouse lawn.
But scruples about separation of church and state vanish for one annual observance.Thanksgiving, that uniquely American holiday, remains the boldest example of what scholars call "civil religion," the nation's collective expression of a vague but ineradicable faith in a nondenominational God.
Many Americans, to be sure, will carve their turkeys without uttering any prayers of gratitude or reciting a Psalm. But many will say grace, and others will offer thanks at worship services.
Officially, the event is defined by the president's annual holiday proclamation. Bill Clinton's nicely wrought proclamations have called upon Americans to gather in homes or houses of worship to express thanks for such blessings as political freedom, patriots and heroes of old, technology, cultural diversity, peace and reduction in nuclear peril.
Clinton has also noted "the bounty and beauty of this great land," the good harvest and the honest toil of farmers.
The Clinton theology is grateful but a bit self-satisfied, reflecting the nation's current prosperous state.
The other obligatory mention in these proclamations regards the Pilgrims of Plymouth, Mass., who were outnumbered by American Indians at the feast of thanks in December 1621, after barely surviving a cruel first year in the New World.
But the Pilgrims were unmentioned in the first presidential proclamation of "a day of publick thanksgiving and prayer," issued by George Washington in 1789, the year the Constitution went into effect. The reasons for his prayer call were the end of the Revolutionary War, the formation of effective national government and the liberties it promised.
In so doing, Washington defined the new nation as monotheistic rather than explicitly Christian. In a classic civil religion formulation, he said thanks were due "that great and glorious Being who is the beneficent Author of all the good that was, that is, or that will be."
The modern Thanksgiving as an annual November observance originated with Abraham Lincoln in 1863. Like 1789, that was a fateful year for the republic. The Emancipation Proclamation had inaugurated the end of human slavery and General Lee's loss at Gettysburg, Pa., seemed to assure that the North would win the Civil War.
In earlier years, Lincoln was a thoroughgoing skeptic about religion, and he never did join a church. But in 1862, when the war was going badly, Lincoln came to believe that defeat was ahead if the conflict was only about saving the Union rather than the higher divine purpose of opposing slavery.
Though Lincoln delivered the Gettysburg Address days before the first modern Thanksgiving, his 1863 Thanksgiving proclamation bears closer resemblance to his other immortal speech, the Second Inaugural Address of 1865.
The 1863 proclamation's strong theme of repentance -- barely mentioned by recent presidents -- is remarkable: "May we not justly fear that the awful calamity of civil war which now desolates the land may be a punishment inflicted upon us for our presumptuous sins, to the needful end of our national reformation as a whole people?"
Though America was blessed with wealth and power, Lincoln declared, "We have forgotten God . . . We have vainly imagined, in the deceitfulness of our hearts, that all these blessings were produced by some superior wisdom and virtue of our own. Intoxicated with unbroken success, we have become too self-sufficient to feel the necessity of redeeming and preserving grace, too proud to pray to the God that made us."
What would be the reaction if a 21st-century U.S. president were to make such a theologically potent statement?