The story
Almost 2,000 years ago, the Roman writer Pliny the Elder filled a giant book, the Natural History, with everything he knew. In it he tells of a recipe found among the papers of King Mithridates of Pontus, said to protect against poison. The last step: “addito salis grano”—with a grain of salt added.
Pliny meant it literally. But much later, scholars writing in Latin took the image and gave it a new life. The phrase “cum grano salis,” with a grain of salt, came to mean accepting a claim with some caution. It is probably medieval Latin, not Pliny’s own words.
English picked it up in the 1600s. In 1609, Thomas Morton wrote of taking something “cum grano salis, with a graine of reasonable salt of better discretion.” By 1647, John Trapp could simply write, “But this is to be taken with a grain of salt.”
Why salt? One idea is that salt makes hard food easier to swallow. Another is that the Latin word sal could also mean good sense and wit. Either way, the grain of salt became a small dose of doubt.
