If "When they're gone they're gone" is just a straight tautology then nobody finds it in the least bit informative. It isn't, because it is tautology. But if it's really not a tautology then that is to say it's metaphorical.
-- Edited by Theodore G. Ammon, Conversations with William H. Gass, 2003
Tautology. Yes, I know, it's an ugly word. But so is the thing. Tautology is this verbal device which consists in defining like by like ("Drama is drama").
-- Roland Barthes, translated by Annette Lavers, Myth Today, 1972
Tautology comes from the Greek tautología, and is formed with tauto- meaning "same" and -logy meaning "writing" or "discourses."