A red herring is a deliberate misdirection and the term comes from hunting. Poachers would interpose themselves between the prey and the hunting party and drag a red herring across the trail to mislead the dogs. This would give them the opportunity to bag the prey themselves. A red herring was chosen because dog trainers often used the pungent, smoked fish to create a trail when training their hounds. The dogs, upon encountering the herring scent, would follow that trail as it was the one they had been trained with.
This excerpt from Nicholas Cox’s 1686 The Gentleman’s Recreation describes the training practice:
The trailing or dragging of a dead Cat, or Fox, (and in case of necessity a Red-Herring) three or four miles...and then laying the Dogs on the scent.
Metaphorical use of red herring, however, doesn’t appear until the late 19th century. From the Liverpool Daily Post of 11 July 1884:
The talk of revolutionary dangers is a mere red-herring.
And this relatively early metaphorical use from the Spectator of 12 March 1890 makes the hunting allusion clear:
These red-herrings drawn across the path.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2014, by David Wilton