Here’s a quote from Bill Bryson’s “The Mother Tongue”:
Imagine being a foreigner and having to learn … , that a sign in the
store saying ALL ITEMS NOT ON SALE doesn’t mean literally what it says
(that every item is not on sale) but rather that only some of the
items are on sale, …
Is this true? Is it a common sign for indicating that not all items are on sale? Wouldn’t it be more natural to write NOT ALL ITEMS ON SALE?
I am asking because I don’t really want to blindly believe Bill Bryson, since his books, although very interesting and entertaining to read, contain a lot of factual errors (intended or not).
I think the answers so far given are concentrating on “on sale”, but I interpret the question to be about the scope of “all” and “not”.
I first noticed, and was troubled by, the usage “all … are not … ” to mean “not all … are … ” about fifty years ago, when I was quite small. Nonetheless, this construction is widely used in English, with this meaning. Furthermore, it is not treated as ambiguous, because to express the “logical” meaning, we would use a different construction with “none” or “no”: “No items are on sale”.
An old example is the proverb “All that glisters is not gold”.
(I agree with you about the unreliability of The mother tongue: he’s a journalist, not a linguist, and it shows. I have recently read another book to which I have the same complaint: Planet Word, by J.P.Davidson)