When we tell someone to take information “with a grain of salt,” we’re recommending a healthy dose of skepticism — to not accept something at face value, or to have some doubt about a claim’s accuracy. But why salt, and why only a grain of it?
This idiom seems to have been around for so long that tracing its precise roots is complicated. But the leading theory goes all the way back to ancient Rome and Pliny the Elder’s encyclopedic 37-volume Naturalis Historia, published between 77 and 79 CE. Pliny recounts the story of how Roman general Gnaeus Pompeius found a poison antidote among the belongings of Mithridates VI, the ruler of the Hellenistic Kingdom of Pontus, following Mithridates’ defeat in 66 BCE. The instructions for the antidote, as described by Pliny, read as follows: “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 Mithridates’ antidote, the grain of salt was quite literal — salt may have been included in the recipe due to the belief it could help neutralize poison, or simply because it would make the antidote more palatable. According to the theory, Pliny’s account of using salt to make poison ineffective became, over the centuries, a fitting metaphor for exercising caution when consuming questionable information. This theory isn’t beyond the realm of possibility, as Pliny’s Naturalis Historia has been studied for centuries — including during the 17th century, when the phrasing “with a grain of salt” reappeared.
According to the Oxford English Dictionary, one of the expression’s first known appearances in written English, in the sense of taking a statement with a certain amount of reserve, comes from John Trapp’s A commentary or exposition upon all the Epistles, which was published in 1647. Written examples of the idiom then became scarce for two centuries, before becoming far more frequent during the late 1800s and through the 20th century, by which time “taking it with a grain of salt” had become commonplace. It has lost Pliny’s literal connotation, yet it still stands as a guard against the poison of misinformation.
More from our network
Word Smarts is part of Inbox Studio, which publishes content that uplifts, informs, and inspires.
