Plagiarism is a crime only where writing is a trade; expression
need never be bound by the law of copyright while it follows thought,
for thought, as some great thinker has observed, is free. The
words were once Shakespeare's; if only you can feel them as he did,
they are yours now no less than his. The best quotations, the best
translations, the best thefts, are all equally new and original
works.
-- Walter Raleigh Style. (1904)