I would like to know the origin of this expression.  Is it biblical?

Hint: Cum grano salis.

The hint really doesn’t help me, as I don’t speak Latin, and haven’t read the Bible in years, if indeed it is of biblical origin, or if it is somehow related to Christ, which was what I thought it might be.

I can’t help with with the origin, I only add the observation that I first came across this as "Take it with a pinch of salt", possibly more common in the UK?

This form also allows one to place even more stress on the required incredulity as:  "Take it with a big pinch of salt".  This doesn’t really work with "grain".

I’ve never heard the word "pinch" used in place of "grain" here in the U.S.  I did notice recently when I saw a British film that the word "pinch" was used to mean "steal."

I’m also confused about the "grain" and the "salt," because salt is a mineral, not a plant.  Although maybe "grain" is referring to a form of measurement.

Brewer’s provides several expressions using salt, several of which are biblical in origin. The biblical expressions, though, all treat salt with a great deal of respect.

The Latin I earlier cited is apparently the origin of our expression, and came about because it’s easier to swallow something that tastes badly (rotten meat?) if taken with a measure of salt.

Interesting.  Although the meaning of the phrase has subsequently been altered to mean "take it lightly" or "don’t take it too seriously."

What is Brewer’s?

Brewer’s Dictionary of Phrase and Fable. First published in England in 1870, it has grown through several revisions to become a fat volume of more than 1,200 pages with tens of thousands of listings.

I believe Harper & Row now publishes a U.S. edition, and that one of the early editions is available online.

UK use is "pinch" of salt. A pinch is the amount you can pick up between the tips of your thumb and forefinger, a small amount.
The same action can be used to pinch a person, by tweeking an exposed area of skin between thumb and forefinger. Done to catch their attention or to show your displeasure! :o
"Pinch" also to steal as a semi-slang expression.

[quote author=dgale link=board=idiom;num=1036689013;start=0#4 date=11/07/02 at 13:58:55]I’m also confused about the "grain" and the "salt," because salt is a mineral, not a plant.  Although maybe "grain" is referring to a form of measurement.

Grain of salt, like grain of sand? By analogy with loose grain or seed, any tiny individual fragment.

Grant

Right, I thought of that, but then was considering grain as a unit of measurement, where one grain equals 0.0648 gram.  Either way, I understand it as a very small (or the smallest?) amount of something.

[quote author=dgale link=board=idiom;num=1036689013;start=0#10 date=11/07/02 at 16:29:09]Either way, I understand it as a very small (or the smallest?) amount of something.

There is a grain of truth in that.  :)

Interesting… Could there be a relationship between salis and salut...?

Bergen Evans to the rescue again.  From Comfortable Words:

When we say of some statement that it must be taken with a grain of salt, we are saying that it must be seasoned a little in order to be "swallowed."  . . .  

It comes from Pliny the Elder’s (A.D. 23-79) account of Mithridates, King on Pontus (120-63 B. C.).  Mithridates, Pliny says, guarded against being poisoned by accustoming his body to poison by small daily doses.  However, he overdid it, because later when he tried to commit suicide by taking poison he found that he was totally immune and had to have a soldier stab him.

Pliny adds that after Mithridates’s death a prescription for an antidote against all poison was found among the king’s possessions.  Unfortunately, Pliny doesn’t give the prescription, but he says that the last line was "to be taken with a grain of salt."

Pliny was one of the most amusing and credulous of men and one of the biggest liars ever known, so the phrase may have picked up some of its meaning from being associated with him.

My understanding was that Plinius (Pliny) used the phrase literally, i e, to add a pinch of salt, and that the metaphorical usag came later.

[quote author=granthutchison link=board=idiom;num=1036689013;start=0#9 date=11/07/02 at 16:15:14]
Grain of salt, like grain of sand? By analogy with loose grain or seed, any tiny individual fragment.

Grant

Sort of . . .

grain n.
. . .
3. a. A relatively small discrete particulate or crystalline mass: a grain of sand.

   b. A small amount or the smallest amount possible: hasn’t a grain of sense.
. . .
with a grain of salt
With reservations; skeptically: Take that advice with a grain of salt.