We're often advised to take things we hear or read with a grain of salt. We understand that this means we should be skeptical about the information, maybe because the source is obviously biased or the facts are unreliable.
Take two dried walnuts, two figs and twenty leaves of rue; pound them all together, with the addition of a grain of salt; if a person takes this mixture fasting, he will be proof against all poisons for that day.
In the original, which is of course in Latin, Pliny wrote "addito salis grano." In modern versions of the Latin phrase, we usually use "cum grano salis," which means "with a grain of salt."
But Pliny means this literally: when mixing this potion against poison, add an actual grain of salt. So when did it become a metaphorical grain of skeptical salt?
The Modern Metaphor
The phrase didn't really pop up again until 1647, when John Trapp used it in his "Commentary on the Old and New Testaments." Specifically, he wrote, "This is to be taken with a grain of salt." The trouble is that scholars aren't quite sure it meant the same thing to Trapp as it means to us now.
There was a period of time after this when the phrase doesn't really seem to have been used; it did pop up occasionally, but it usually referred to actual grains of salt. But in 1908, "The Athenaeum," an American literary journal included this line: "Our reasons for not accepting the author's pictures of early Ireland without many grains of salt." You have to feel a little bad for that author learning that his photography skills weren't up to the standards of this magazine through the use of this fresh, new idiom.
It does seem that the modern meaning of the phrase is American, as the Brits seemingly picked up the similar "with a pinch of salt" only after World War II. The earliest printed British citation seems to be found in F.R. Cowell's "Cicero & the Roman Republic," from 1948:
"A more critical spirit slowly developed, so that Cicero and his friends took more than the proverbial pinch of salt before swallowing everything written by these earlier authors."
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