US Constitution, Amendment I: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances."
There IS no mention of "separation of church and state" ANYWHERE in the US Constitution! These is NOTHING there that says you can't mention God, ANYWHERE. What it does is forbid the government from establishing an official religion, but also prohibits government actions that unduly favor one religion over another. It also prohibits the government from unduly preferring religion over non-religion, or non-religion over religion. PERIOD.
The rest simply says Congress can't restrict Speech, the Press, prevent you from gathering together and if the federal government is exceeding the authority granted to it under the constitution, the people have a right to formally complain and the government must respond.
http://www.law.cornell.edu/constitution/first_amendmentHere is a link to Supreme Court notable cases dealing with the First Amendment, Obscenity and Indecency. Miller v. California, 413 U.S. 15, 93 S.Ct. 2607, 37 L.Ed.2d. 419 (1973) is where the court mapped out a three part test for what is obscene. "First, the average person, applying contemporary community standards, must find that the work, taken as a whole, appeals to prurient interests; second, that it depicts or describes, in a patently offensive way, sexual conduct as defined by state law; and third, that the work, taken as a whole, lacks serious literary, artistic, political, or scientific value."
http://www.ala.org/advocacy/intfreedom/censorshipfirstamendmentissues/courtcasesNotable First Amendment Court Cases:
This page contains summaries of frequently cited First Amendment cases. Arranged by topic, they cover case law issued by a variety of courts: the Supreme Court of the United States, the Court of Appeals of different Federal circuits, the District Court of several Federal districts, as well as the highest court of several states and particular appellate courts of action.
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