Out of the Blue

Shortened from the fuller "a bolt from the blue," the image of lightning striking from a clear blue sky rather than the dark storm clouds it normally comes from, making it a natural symbol for a completely unforeseen event. Scottish writer Thomas Carlyle recorded the fuller phrase in his history The French Revolution (1837), likely drawing on the classical Roman poet Horace, whom Carlyle had studied closely. The shortened "out of the blue" followed in 1879, in the magazine The Spectator. A separate, less-supported theory connects the phrase instead to a crossbow bolt fired from an unseen distance.