The "Lemon Test".

Alton Lemon is an "honorary officer" of the Freedom From Religion Foundation, a position reserved for freethinkers who have won Supreme Court cases in favor of the separation of church and state. He received a "Hero of the First Amendment" award at the 2003 FFRF convention (although health problems at the last minute prevented him from accepting it in person). Alton Lemon won the case, Lemon v. Kurtzman, 1971, which successfully challenged a Pennsylvania law, the first such law in the nation providing public tax funds to religious schools for teaching four secular subjects. As a member of the ACLU, Mr. Lemon volunteered to challenge the law, which resulted in a decision that is a watershed for the Establishment Clause, and which historic decision bears his name. The United States Supreme Court unanimously invalidated the parochial aid. In one of the enduring legacies of the Burger Court, it also codified existing precedent on the Establishment Clause into a test--called the "Lemon Test." Despite attacks against it and attempts to modify and chip away at it, the Lemon Test endures.

“If any of the three prongs of the Lemon Test are violated by an act of government, it is unconstitutional:

1) It must have a secular legislative purpose;

2) Its principal or primary effect must neither advance nor inhibit religion;

3) It must not foster excessive entanglement between government and religion.”

-- The Lemon Test, promulgated in Lemon v. Kurtzman, 403 US 602 (1971)