An idea is a light turned on in a man's soul. Comic-strip artists are in the habit of representing it by means of a light bulb flashing on, above the head of a character who has suddenly grasped an idea. In simple, primitive terms, this is an appropriate symbol.
Ayn Rand, Nathaniel Branden, Alan Greenspan, Robert Hessen (1986). “Capitalism: The Unknown Ideal”, p.289, Penguin
