Freedom of thought, which includes freedom of religious belief, is basic in a society of free men. It embraces the right to maintain theories of life and of death and of the hereafter which are rank heresy to followers of the orthodox faiths. Heresy trials are foreign to our Constitution. Men may believe what they cannot prove. They may not be put to the proof of their religious doctrines or beliefs. Religious experiences which are as real as life to some may be incomprehensible to others.

William O. Douglas (1898-1980) US Supreme Court justice (1939-75)

Majority opinion, United States v. Ballard, 322 U.S. 78 (1944)

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