Everyone knows the Supreme Court ruled that one kind of Ten Commandments display on government property is unconstitutional, but that another kind is acceptable. But no one—including the Supreme Court itself—seems to be able to explain why.

"Commandments may be displayed in state capitols but not in courthouses," said a National Council of Churches press release—wrongly. But cnn initially made the same mistake.

So guess which display won approval: Was it the six-foot granite monolith inscribed with a Christian Chi-Rho symbol and "I AM the LORD thy God" in extra-large letters? Or was it the framed paper copy of Exodus 20:3-17 from the King James Version displayed along with the Magna Carta, the Declaration of Independence, the Bill of Rights, and other items—along with the explanation that "The Ten Commandments have profoundly influenced the formation of Western legal thought"?

That the Supreme Court found the first display (in Texas) acceptable and the second (in Kentucky) unacceptable perfectly illustrates the near-total lack of consistency in church-state rules.

In fact, right now there are no rules. "Establishment Clause doctrine lacks the comfort of categorical absolutes," the five-justice majority ruled in the Kentucky case (McCreary County v. ACLU). "Tradeoffs are inevitable, and an elegant interpretive rule to draw the line in all the multifarious situations is not [to] be had."

It sounds "enlightened" and nuanced, but the decisions don't even agree on the basics. In McCreary, the Court ruled, "the government may not favor … religion over irreligion." In the Texas case (Van Orden v. Perry) the same day, the Court ruled, "we … do not adhere to the principle that the Establishment Clause bars ...