To be skeptical about something or not believe it entirely; to view information with doubt or reservation.
This phrase traces back to ancient times and Pliny the Elder's 'Natural History' (77 AD), where he mentioned that an antidote to poison could be made effective by taking it 'cum grano salis' (with a grain of salt). The idea was that salt could make even something harmful more palatable or safe. The English version emerged in the 1600s.
Salt has been precious throughout human history - Roman soldiers were sometimes paid in salt (hence 'salary'), and it was essential for food preservation before refrigeration. The phrase cleverly suggests that just as salt makes unpalatable food edible, a bit of skepticism makes dubious information digestible without being harmful.
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